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Full text of "Organic chemistry"

ORGANIC CHEMISTRY 



NEW AND REVISED EDITION 



BY 
W.^H. PERKIN, JUN., PH.D., F.R.S. 

PROFESSOR OF ORGANIC CHEMISTRY IN THE OWENS COLLEGER MANCHESTER 
- AND 

F. STANLEY KIPPING, PH.D., D.Sc. (LOND.), F.R.S. 

PROFESSOR OF CHEMISTRY IN UNIVERSITY COLLEGE, NOTTINGHAM 




W. & E. CHAMBERS, LIMITED 

LONDON AND EDINBURGH 
1904 



Edinburgh : 
Printed by W. & R. Chambers, Limited. 



PREFACE. 



OUR original intention was to write a small text-book on 
Organic Chemistry, based on the syllabus drawn up by the 
Science and Art Department, in the hope that it would be 
useful to students attending the elementary or advanced 
classes in the subject, and not without value to teachers 
as a handy book of reference. As, however, it soon became 
apparent that, by making comparatively few additions, the 
subject-matter might be made to include the facts usually 
dealt with in a course of about sixty lectures, the scope 
of the work was enlarged to this extent, so as at the 
same time to make it more useful to general students as 
an introduction to Organic Chemistry. 

Part I., which deals with the fatty compounds, contains, in 
the first place, a general account of the methods most fre- 
quently employed in the separation, purification, and analysis 
of organic compounds, and in the determination of molecular 
weight. The preparation and properties of typical com- 
pounds are then described, attention being directed to those 
changes which come under the heading of general reactions 
rather than to isolated facts regarding particular substances. 
Questions of constitution are also discussed at some length, 



v PREFACE. 

and in the case of most of the typical compounds, the facts 
on which the given constitutional formula is based are specific- 
ally mentioned. This course was adopted, not only in order 
to avoid the introduction of a long chapter on structure at an 
earlier stage, but also because, in our opinion, a constant 
use of constitutional formula?, accompanied by a clear con- 
ception of their meaning, is one of the greatest helps, even to 
a beginner, in committing the facts to memory. 

The opening chapters of Part II. contain an account of coal- 
tar and its treatment. This leads naturally to a description of 
the preparation and properties of benzene, and to a discussion 
of its constitution in the light of facts previously dealt with ; 
the student is thus made acquainted with the principal 
characteristics of aromatic, as distinct from fatty, compounds, 
and is then in a position to understand the classification of 
organic substances into these two main divisions. 

The more important classes of aromatic compounds are then 
described, but in a somewhat different manner from that 
adopted in Part L, inasmuch as a general account of the 
properties of each class of substances is given before, instead 
of after, the more detailed description of typical compounds ; 
this course is to a great extent free from the disadvantages 
which are found to attend its adoption at earlier stages, as the 
student has by this time acquired some experience of the more 
systematic method from a study of the summaries given in 
Part I. 

Special attention has been given, as before, to questions of 
constitution, one of the objects- being to train the student to 
think out such matters, and to try and deduce a constitutional 
formula for a given substance, by comparing its properties with 
those of others of known constitution ; with this end in view, 
it has often been thought desirable to withhold the most 



PREFACE. t 

important evidence in favour of the accepted constitutional 
formula until the subject had been discussed at some length. 

The concluding chapters on dyes, alkaloids, and stereo- 
isomerism will doubtless offer the greatest difficulties, but, 
considering the importance of the matters with which they 
deal, their omission or curtailment was deemed inadvisable. 
The account of the alkaloids should be useful, more particu- 
larly to medical students, whilst the chapter on dyes deals 
with a variety of substances of even greater practical value, 
and indicates the methods employed in one of the most im- 
portant applications of organic chemistry. The chapter on 
stereo-isomerism was included because, owing to the import- 
ance to which this theory has now attained, a text-book on 
organic chemistry would be incomplete without a brief dis- 
cussion of the subject. The full directions which are given 
for the use of models will, it is hoped, lead to a clear con- 
ception of the views set forth. 

A considerable proportion of the text, dealing as a rule 
either with matters of less importance or of a more advanced 
nature, is printed in small type, and should be left out of 
consideration until the rest of the subject-matter has been 
mastered, or, at any rate, studied. The consideration of the 
'summary and extension' at the conclusion of some of the 
more important chapters, should also be postponed until the 
student has acquired some knowledge of the subject, as the 
method here adopted is not well suited to the requirements 
of a beginner. 

One of the principal objects throughout has been to treat 
the subject from a practical point of view (as far as this could 
be done in a text-book on theoretical chemistry), because, un- 
less a thorough course of practical work accompanies the 
theoretical, no really satisfactory progress can be made. The 



VI PREFACE. 

student should himself perform many of the simple exercises 
involved in the purification and analysis of organic com- 
pounds, and should prepare typical substances in order to 
become practically acquainted with their properties. Such 
general operations as oxidation, reduction, hydrolysis, nitra- 
tion, sulphonation, &c., and the more important general 
reactions for the identification of the several classes of com- 
pounds, should also be included in the practical course. 

In many respects we have made free use of the excellent 
text-books of V. Meyer and Jacobson and von Richter, of 
Beilstein's Handbuch, and of Ost's Lehrbuch der technischen 
Cliemie. We are also much indebted to Dr A. Harden for 
help in revising the proof-sheets, and in preparing the index. 



Since this preface was written, a chapter dealing with some 
of the more important constituents of plants and animals has 
been added in the form of an Appendix, with a separate 
index. We hope that this new chapter will be found useful 
by all readers, but especially by medical students, for whom 
more particularly it has been written. 



PREFACE TO REVISED EDITION. 



THE favourable reception accorded to our Text-book on 
Organic Chemistry, and the constantly increasing support 
which it has received during recent years, have led us to 
undertake already a complete revision of Parts I. and II. 
in order to bring the whole of the subject-matter thoroughly 
up-to-date. Although, in doing so, we have not introduced 
any noteworthy change in the general plan of the work, 
we have found it necessary to make throughout many 
alterations of considerable importance in order to take 
account of the new facts and views which have come 
into prominence in the course of the rapid and continued 
progress of Organic Chemistry. Certain chapters, indeed, 
have been almost entirely rewritten and numerous additions 
have been made, but as it has also been possible to omit 
or condense portions of the old text dealing with matters 
of diminishing importance, the size of the book has not 
been very materially increased ; we trust, therefore, that 
the revised edition will prove useful to the same classes 
of students as those for whom the original one was intended. 



ARITHMETIC, Theoretical and Practical. By J. S. MACKAY, M.A., LL.D., 
Author of ' Mackay's Euclid.' 4/6. 

ALGEBRA FOR SCHOOLS. By WILLIAM THOMSON, M.A., B.Sc., Registrar, 
University of the Cape of Good Hope, formerly Assistant-Professor of Mathe- 
matics and Mathematical Examiner, University of Edinburgh. 576 pages. 
Cloth, 4/6. 

CHAMBERS'S ELEMENTARY ALGEBRA. By WILLIAM THOMSON, M.A., 
B.Sc. Up to and including Quadratic Equations. 288 pages. Cloth, 2/. 
With Answers, 2/6. 

THE ELEMENTS OP EUCLID. Books I. to VI., and parts of Books XI. and 
XII. With Numerous Deductions, Appendices, and Historical Notes, by 
J. S. MACKAY, LL.D., Mathematical Master in the Edinburgh Academy. 
412 pages. 392 diagrams. 3/6. Separately, Book I., I/; II., 6d. ; III., 9d. ; 
Books XL XII., 6d. Key, 3/6. 

MATHEMATICAL TABLES. By JAMES PRYDE, F.E.I.S. These comprehend 
the most important Tables required in Trigonometry, Mensuration, Land- 
Surveying, Navigation, Nautical Astronomy, &c. The tables of Logarithms 
(1 to 108000), Logarithmic Sines, &c., are carried to seven decimal places. 
496 pages. 4/6. 



CONTENTS. 



PAGE 

CHAPTER I. COMPOSITION, PURIFICATION, AND ANALYSIS OF 

ORGANIC COMPOUNDS 1 

Origin and Present Meaning of the Word Organic ' 1 

Composition of Organic Compounds 3 

General Principles of Organic Analysis 4 

Separation and Purification of Organic Compounds 4 

Tests of Purity 12 

Qualitative Elementary Analysis 14 

Quantitative Elementary Analysis 18 

Estimation of Carbon and Hydrogen 18 

Quantitative Determination of Nitrogen 23 

Quantitative Determination of Chlorine, Bromine, and 

Iodine 27 

CHAPTER II. DEDUCTION OF A FORMULA FROM THE RESULTS 
OF ANALYSIS AND DETERMINATION OF MOLECULAR 

WEIGHT 30 

CHAPTER III. CONSTITUTION OR STRUCTURE OF ORGANIC 

COMPOUNDS 48 

CHAPTER IV. THE PARAFFINS, OR HYDROCARBONS OF THE 

METHANE SERIES 53 

Methane, or Marsh-gas 53 

Ethane 58 

Propane 60 

Butanes 61 

Pentanes 63 

Isomerism 64 

Homologous Series 66 

General Formulae 66 

Summary and Extension 67 



X CONTENTS. 

PAGE 

CHAPTER V. UNSATURATED HYDROCARBONS THE OLEFINES, 

OR HYDROCARBONS OF THE ETHYLENE SERIES 71 

Ethylene 71 

Propylene 78 

Summary and Extension 79 

Hydrocarbons of the Acetylene Series 80 

Acetylene 81 

Allylene Crotonylene 87 

Summary and Extension 89 

CHAPTER VI. THE MONOHYDRIC ALCOHOLS 89 

Methyl Alcohol 89 

Ethyl Alcohol 94 

Production of Wines and Beers; Alcoholic Fermentation... 97 

Homologues of Ethyl Alcohol 103 

Propyl Alcohol Isopropyl Alcohol 105 

Butyl Alcohols Amyl Alcohols 106 

Summary and Extension 107 

CHAPTER VII. THE ETHERS , Ill 

Methyl Ether Ill 

Ethyl Ether Ill 

Summary and Ex tension 115 

Radicles 116 

CHAPTER VIII. ALDEHYDES AND KETONES 118 

^ Formaldehyde 118 

^ Polymerisation 121 

--pA.cetaldehyde 122 

Polymerisation of Acetaldehyde 126 

Acetal Chloral 127 

Homologues of Acetaldehyde 129 

Ketones 130 

Acetone 130 

Condensation of Acetone 133 

Hydroximes and Hy d razones 1 34 

Summary and Extension 136 

CHAPTER IX. THE FATTY ACIDS 145 

^ Formic Acid 145 

Acetic Acid 149 



CONTENTS. XI 

PACK 

Homologues of Acetic Acid 156 

Propionic Acid 158 

Normal Butyric Acid 1 58 

Isobuty ric Acid Iso valeric Acid 1 59 

Normal Heptylic Acid 160 

^Palmitic Acid Stearic Acid 160 

Derivatives of the Fatty Acids Acid Chlorides 161 

Anhydrides 162 

Acetic Anhydride 1 63 

./Amides 164 

Acetamide 1 64 

Substitution Products of Acetic Acid 165 

Chlor-, Dichlor-, and Trichlor-acetic Acid 166 

Summary and Extension 167 

Fats, Oils, Soaps, Stearin, and Butter 169 

Composition of Fats and Oils 169 

Soaps 171 

Stearin and Glycerol 1 72 

Butter 173 

CHAPTER X. ETHEREAL SALTS, OR ESTERS 174 

Halogen Ethereal Salts and Halogen Derivatives of the 

Paraffins Methyl Chloride 174 

Methylene Dichloride Chloroform 175 

Carbon Tetrachloride ....177 

lodoform Ethyl Chloride 178 

Ethyl Bromide 179 

Ethyl Iodide 180 

Ethereal Salts of Nitric Acid Ethyl Nitrate 182 

Ethereal Salts of Nitrous Acid Ethyl Nitrite 183 

Nitro-paraffins 184 

Ethereal Salts of Sulphuric Acid 185 

Ethyl Hydrogen Sulphate 185 

Mercaptans and Sulphides 1 86 

Ethyl Mercaptan 187 

Ethyl Sulphide 188 

Ethereal Salts of Organic Acids Ethyl Acetate 188 

Summary and Extension 190 



Xll CONTENTS. 

PAGE 

CHAPTER XL SYNTHESIS OF KETONES AND FATTY ACIDS 
WITH THE AID OF ETHYL ACETOACETATE AND ETHYL 

MALONATE 193 

Ethyl Acetoacetate 193 

Ketonic Acids 200 

Ethyl Malonate 201 

CHAPTER XII. ALKYL COMPOUNDS OF NITROGEN, PHOS- 
PHORUS, ARSENIC, SILICON, ZINC, MERCURY, AND 

OTHER ELEMENTS 204 

Ethylamine 205 

Diethylamine 208 

Triethylainine 209 

Tetretliylammonium Hydroxide 210 

Preparation and Identification of Amines 211 

Phosphines 214 

Arsines 215 

Trie thy larsine Tetrethylarsonium Iodide 216 

Dimethylarsine Oxide 217 

Organic Silicon Compounds 218 

Silicon Tetramethyl Silicon Tetrethyl 219 

Organo- metallic Compounds 220 

Zinc Ethyl 220 

Mercuric Ethyl 222 

CHAPTER XIII. THE GLYCOLS AND THEIR OXIDATION PRO- 
DUCTS 223 

Ethy lene Glycol 224 

Oxidation Products of the Glycols Glyoxal 229 

Hydroxycarboxylic Acids Glycollic Acid 229 

Lactic Ac^d 231 

Hydracrylic Acid 233 

Dicarboxylic Acids 234 

Oxalic Acid 235 

Oxamide 239 

Malonic Acid 239 

SuccinicAcid 240 

Succinic Anhydride 241 



CONTENTS. Xlll 

PAGE 

Hydroxydicarboxy lie Acids Malic Acid 245 

Tartaric Acid 247 

Hyd roxy tricarboxylic Acids Citric Acid 251 

CHAPTER XIV. TKIHYDRIC AND POLYHYDRIC ALCOHOLS 253 

Glycerol 254 

Chlorohydrins 257 

Nitro-glycerin 258 

Unsaturated Compounds related to Glycerol 260 

Allyl Alcohol 260 

Allyl Iodide 261 

Allyl Bromide Allyl Sulphide Acrole'in 262 

Acrylic Acid 263 

Polyhydric Alcohols Ery thritol - Mannitol 264 

CHAPTER XV. THE CARBOHYDRATES 266 

Monoses Glucose 267 

Mannose Galactose 269 

Fructose 270 

Action of Phenylhydrazine on Glucose and Fructose 272 

Bioses Sucrose 274 

Maltose 276 

Lactose 277 

Polyoses Starch 278 

Gluten Dextrin 280 

Cellulose 281 

Gun-cotton Cordite Collodion 282 

Summary and Extension 283 

CHAPTER XVI. CYANOGEN COMPOUNDS : 285 

Cyanogen 285 

Hydrogen Cyanide 287 

Potassium Ferrocyanide 292 

Potassium Ferricyanide 293 

Nitriles 293 

Cyanic Acid 295 

Thiocyanic Acid 296 

Allyl Isothiocyanate 298 



XIV CONTENTS. 

PAGE 

CHAPTER XVII. AMIDO- ACIDS GLYCINE 299 

^^rea, 301 

Uric Acid 303 

CHAPTER XVIII. MANUFACTURE, PURIFICATION, AND PRO- 
PERTIES OF BENZENE 305 

CHAPTER XIX. CONSTITUTION OF BENZENE, AND ISOMERISM 

OF BENZENE DERIVATIVES 313 

CHAPTER XX. GENERAL PROPERTIES .OF AROMATIC COM- 
POUNDS 331 

Classification of Organic Compounds 331 

General Character of Aromatic Compounds 334 

CHAPTER XXL HOMOLOGUES OF BENZENE AND OTHER 

HYDROCARBONS 339 

Toluene Xyleiies Mesitylene Cumene Cymene 344-349 

Diphenyl Diphenyl methane Triphenylmethane 350 

CHAPTER XXII. HALOGEN DERIVATIVES OF BENZENE AND 

ITS HOMOLOGUES 352 

Chlorobenzene Bromobenzene lodobenzene lodoso- 
benzene lodoxybenzene Chlorotoluene Benzyl 
Chloride 357-361 

CHAPTER XXIII. NITRO-COMPOUNDS 362 

Nitrobenzene Meta-dinitrobenzene Nitrotoluenes 365-367 

CHAPTER XXIV. AMIDO-COMPOUNDS AND AMINES 367 

Aniline and its Derivatives 373 

Homologues of Aniline Alkylanilines.... 376, 377 

Diphenyl amine and Triphenylamine 379 

Aromatic Amines Benzylamine 380 

CHAPTER XXV. DIAZO-COMPOUNDS AND THEIR DERIVA- 
TIVES 381 

Diazoamido- and Amidoazo-compounds 386 

Phenylhydrazine 388 

Azo- and Azoxy-compounds 390 

CHAPTER XXVI. SULPHONIC ACIDS AND THEIR DERIVA- 
TIVES..., ...392 



CONTENTS. XV 

PAGE 

CHAPTER XXVII. PHENOLS 398 

Monohydric Phenols Phenol Picric Acid Cresols 404-409 

Dihydric Phenols Gatechol, Resorcinol, Hydroquinone..410,411 
Trihydric Phenols 412 

CHAPTER XXVIII. AROMATIC ALCOHOLS, ALDEHYDES, 

KETONES, AND QUINONES 414 

<? Alcohols Benzyl Alcohol 414, 415 

5 Aldehydes Benzaldehyde 417, 418 

Hydroxy-aldehydes Salicy lahlehyde 421, 422 

^ ~>Ketones Acetophenone 423 

Quinones Qninone 425 

CHAPTER XXIX. CARBOXYLIC ACIDS 428 

Benzoic Acid Benzoyl Chloride Benzoic Anhydride 

B.enzamide Benzonitrile 430-433 

Substitution Products of Benzoic Acid 434 

Tolnic Acids 435 

Dicarboxylic Acids Phthalic Acid, Phtlialic Anhydride, 

Isophthalic Acid, Terephthalic Acid 436-440 

Phenylacetic Acid, Phenylpropionic Acid, and Derivatives.. 440 
Cinnamic Acid '. 443 

CHAPTER XXX. H YDROX YC ARBOX YLIC ACIDS 446 

Salicylic Acid Anisic Acid Protocateclmic Acid Gallic 
Acid Tannin Mandelic Acid 450-453 

CHAPTER XXXI. NAPHTHALENE AND ITS DERIVATIVES 454 

Naphthalene 455 

Naphthalene Tetrachloride Nitro-derivatives Amido- 
derivati ves Naphthols Sulphonic Acids a-Naph- 
thaquinone /3-Naphthaquinone 463-469 

CHAPTER XXXII. ANTHRACENE AND PHENANTHRENE 470 

Anthracene 470 

Anthraquinone Alizarin Phenanthrene Phenanthra- 
quinone Diphenic Acid 475-484 

CHAPTER XXXIII. PYRIDINE AND QUINOLINE 484 

Pyridine and its Derivatives 485 

Piperidine 489 



XVI CONTENTS. 

PAGE 

Homologues of Pyridine Pyridinecarboxylic Acids 491 

Quinoliiie 493 

Isoquinoline 496 

CHAPTER XXXIV. ALKALOIDS 497 

Alkaloids derived from Pyridine 501 

Alkaloids derived from Quinoline 504 

Alkaloids contained in Opium Morphine, &c 508 

Alkaloids related to Uric Acid Caffeine, &c 510 

Antipy line 511 

Choline, Betai'ne, Neurine, and Taurine 513 

CHAPTER XXXV. DYES AND THEIR APPLICATION 514 

Malachite Green, Pararosaniline, Rosaniline, Methylviolet, 

Aniline Blue 521-529 

The Phthaleins Phenolphthalein, Fluorescei'n, Eosin.. 530-532 
Azo-dyes Aniline Yellow, Chrysoidine, Bismarck Brown, 

Helianthin, Resorcin Yellow, Rocellin, Congo-red, 

Benzopurpurins 533-538 

Various Colouring Matters Martius' Yellow, Methylene 

Blue, Indigo 538-540 

CHAPTER XXXVI. OPTICAL- AND STEREO-ISOMERISM 541 

APPENDIX. THE CONSTITUENTS OF PLANTS AND ANIMALS... 561 
Carbohydrates Glucosides Essential Oils Terpenes.. 563-586 
Lecithine Ptomaines Purine Derivatives Amido-acids 
Bile Products Haemoglobins Prote'ids 587-615 

INDEX 617 

INDEX TO APPENDIX... 633 



ORGANIC CHEMISTRY. 



PART I. 



CHAPTER I. 

COMPOSITION, PURIFICATION, AND ANALYSIS OF ORGANIC 
COMPOUNDS. 

Origin and Present Meaning of the Word 'Organic.' 

Although spirit of wine, sugar, fats, and many other sub- 
stances obtained directly or indirectly from animals or plants 
have been known from the earliest times, their investiga- 
tion made but little progress until towards the close of the 
eighteenth century, when the composition of many of these 
natural products was established by the French chemist 
Lavoisier (1743-94). Lavoisier it was who first showed that, 
in spite of their great number, nearly all vegetable substances 
are composed of carbon, hydrogen, and oxygen, whilst animal 
substances, although also consisting for the most part of the 
same three elements, frequently contain nitrogen, and some- 
times phosphorus and sulphur. 

This peculiarity in composition, and probably also the fact 
that these natural products behaved differently from mineral 
compounds in being combustible, led to the belief that all 
animal and vegetable substances were produced under the 
influence of a peculiar vital force, and that their forma- 
tion was regulated by laws quite different from those which 

A 



COMPOSITION, PURIFICATION, AND ANALYSIS 

governed the formation of mineral substances ; consequently, 
it was thought impossible to prepare any animal or vegetable 
product artificially or synthetically in the laboratory. 

For these reasons compounds obtained from animals and 
plants that is to say, directly or indirectly from living 
organisms were called organic, and were classed separately 
from inorganic or mineral substances. 

This distinction between organic and inorganic compounds 
appears to have been generally accepted until 1828, when 
Wohler succeeded in obtaining urea, an excretion of certain 
animal organisms, from ammonium cyanate, a substance which 
was at that time considered to be inorganic or mineral, 
because it could be produced in the laboratory ; this synthesis 
showed conclusively that the influence of a living organism 
was not necessary for the production of the ' organic ' sub- 
stance urea. 

After this important discovery it was soon found that 
many other so-called * organic ' substances could be prepared 
in the laboratory from ' inorganic ' materials, and ultimately it 
caine to be generally acknowledged that the formation of 
all ' organic ' as well as that of ' inorganic ' compounds is 
absolutely independent of the help of a 'Vital force.' 

The supposed difference between the two classes of com- 
pounds having thus been recognised as purely an imaginary 
one, the terms ' organic ' and ' inorganic ' lost, of course, their 
original meaning ; they are, nevertheless, still made use of in 
the classification of chemical compounds for the following 
reasons : 

(1) The compounds containing carbon which are already 
known are far more numerous than the known compounds of 
any other element. (2) These carbon compounds are related 
to one another, and differ widely in general behaviour from 
those of other elements ; they form, in fact, a special group 
by themselves. It is convenient, therefore, to class them 
separately, and to distinguish them by the term organic, 
which recalls the- fact that carbon is a most important 



OF ORGANIC COMPOUNDS. 3 

4 

constituent of all animal and vegetable substances; organic 
chemistry, therefore, is the chemistry of the carbon com- 
pounds. 

Some of the simpler compounds of carbon, such as carbon 
dioxide, carbon monoxide, carbon disulphide, &c., which are 
of general importance, are always described in works on 
inorganic chemistry for the sake of convenience; they are, 
nevertheless, organic compounds, because they contain carbon. 

The reasons why so many carbon compounds are known are 
not far to seek. All the chief constituents of animals and 
plants are derivatives of carbon, and many of them occur 
in extraordinary abundance ; each of these naturally occur- 
ring compounds forms a starting-point from which many 
others can be obtained artificially with the aid of heat or by 
chemical action ; these new substances, in their turn, serve as 
materials for further investigation. 

Another reason why carbon compounds are so numerous is 
that the atoms of carbon are distinguished from those of all 
other elements by their extraordinary capability of combining 
with one another and with hydrogen to form compounds, such 
as CH 4 , C 6 H 6 , C 10 H 8 , &c., the molecules of which are often 
composed of a very large number of atoms ; other elements 
rarely combine with hydrogen to form more than one or two 
compounds, and their atoms seem to possess only to a very 
limited extent the power of combining with one another. 

Composition of Organic Compounds. In spite of their 
great number, most organic compounds are made up of not 
more than four or five elements. 

Those, such as sugar, starch, and tartaric acid, which occur 
in the vegetable kingdom generally consist of carbon, 
hydrogen, and oxygen, although a few morphine and strych- 
nine, for example contain nitrogen as well. Those occurring 
in the animal kingdom generally contain nitrogen as well as 
carbon, hydrogen, and oxygen : urea and uric acid, for in- 
stance, are composed of these four elements ; a few vegetable 
and animal substances also contain sulphur and phosphorus. 



4 COMPOSITION, PURIFICATION, AND ANALYSIS 

Artificially prepared organic compounds may contain any 
element. Some benzene, for example are composed of 
carbon and hydrogen only, but most of them contain oxygen 
as well ; nitrogen, sulphur, and the halogens are very often 
present in carbon compounds produced in the laboratory ; so 
also are the metals calcium, sodium, silver, &c., which form 
salts with organic, just as they do with inorganic, acids. 

General Principles of Organic Analysis. The qualitative 
analysis of organic compounds is carried out by methods quite 
different from those employed in the case of inorganic sub- 
stances. Many organic compounds are insoluble in water 
and in acids, and could not be^ examined by the ordinary 
wet methods of analysis : eyen those which are soluble do 
not show, except in rare cases, a sufficiently characteristic 
behaviour to enable them to be identified by such methods. 
There is, again, this wide difference between inorganic and 
organic analysis, that, whereas a mixture of inorganic com- 
pounds may be directly submitted first to qualitative and 
then to quantitative examination, in the case of a mixture 
of carbon compounds it is nearly always necessary to 
separate and purify each constituent before even its qualita- 
tive composition can be determined. 

For these reasons organic analysis usually consists of several pro- 
cesses : Firstly, the substance is submitted to a preliminary quali- 
tative examination, the object of which is to find out how many 
distinct compounds are present, and to separate and purify each of 
them. The nature of each constituent is then determined ; this 
may sometimes be done by proving it to be identical with some 
known compound by methods to be described later. If this be 
impossible, a further qualitative examination is made to ascertain 
what elements the substance contains ; the pure compound is then 
submitted to quantitative or elementary analysis, from the results 
of which its percentage composition is obtained. 

Separation and Purification of Organic Compounds. 

The separation of a pure organic compound from a mixture 
of any kind is often a matter of considerable difficulty, and it 
is usually necessary to employ different processes for different 



OP ORGANIC COMPOUNDS. 



mixtures. Although, therefore, it is impossible to give a 
method which would be applicable in every case, the more 
important processes used in the separation and purification of 
organic substances may be briefly indicated. 

In the case of any substance of unknown nature, a small 
portion is first ignited on platinum foil ; if it leave a non- 
combustible residue, it is probably a salt of some organic acid, 
or it contains inorganic compounds as impurity. 

The separation of an organic from an inorganic substance 
can usually be accomplished by shaking or warming the sub- 
stance with some solvent, such as alcohol, ether, benzene, 
chloroform, petroleum, &c. Most organic compounds are 
soluble in one or other of these liquids, whereas inorganic 
compounds, as a rule, are insoluble, or nearly so. "Water 
or dilute acids may often be employed for the same pur- 



pose, since many 



sub- 



stances are soluble, many organic 
substances insoluble, in these 
liquids. 

The separation of two or more 
organic substances may sometimes 
be effected in a similar manner. 
In the case of a mixture of cane- 
sugar, tartaric acid, and benzoic 
acid, for example, the last-named 
compound only can be dissolved 
out with ether, the tartaric acid 
being then separated from the 
sugar by treating with alcohol, 
m which it is much more readily 
soluble than sugar. 

Solid or liquid organic sub- 
stances in aqueous solution, or 
suspended in water in a fine state of division, may often 
be isolated by agitating the solution or mixture with some 
solvent, such as ether, benzene, chloroform, &c., which does 




Fig. 1. 



6 COMPOSITION, PURIFICATION, AND ANALYSIS 

not mix with water. For this purpose a separating funnel 
(fig. 1) is employed, and after having been shaken vigorously, 
the mixture is left at rest until it forms two layers ; the two 
solutions are then separated by turning the tap (a, a') and 
running off that which is underneath, the extraction being 
repeated, if necessary, with a fresh quantity of the organic 
solvent. The combined extracts are then dried (p. 10), and 
the solvent distilled or slowly evaporated. 

In extracting with ether it is usually advisable to first saturate 
the aqueous solution with sodium chloride, calcium chloride, or 
some other readily soluble salt, in order to lessen the solubility 
of the ether in the water, and also that of the organic compound 
which is to be extracted ; this process is called ' salting out. ' 

The process of crystallisation is one of the best methods 
of separating and purifying solid organic substances, but 
before it can be successfully employed a suitable solvent 
must be found. About a centigram of the substance is 
placed in a test tube with 1-2 c.c. of some solvent (such as 
water, ether, alcohol, carbon bisulphide, benzene, light petro- 
leum, &c.), and after boiling for a few moments* the hot 
liquid is allowed to cool ; if then the substance be deposited 
in crystals, the solvent may be regarded as suitable, and the 
rest of the material is treated in the same way, the insoluble 
portion, if any, being examined separately. Should no 
separation of crystals take place on cooling, the solution is 
concentrated by evaporation, and then allowed to cool; if, 
again, crystals be not deposited, some other solvent is tried. 
The crystals ultimately obtained are collected on a filter or 
on a piece of unglazed earthenware, washed with a small 
quantity of the solvent, and further purified by recrystallisa- 
tion if necessary. 

If only one constituent of a mixture be dissolved by the 
liquid employed, this particular substance is obtained in a 
state of purity without difficulty, because the others are 

* In working with highly inflammable liquids great caution is necessary 
to avoid serious accidents. 



OP ORGANIC COMPOUNDS. 7 

easily got rid of by filtration; when, however, two or more 
of the constituents are soluble, their further separation can 
usually be effected by fractional crystallisation. In this 
process, advantage is taken of the difference in solubility of 
the substances. On slowly cooling a hot solution of two (or 
more) substances, one of them is often deposited in crystals 
before the other, and can then be separated by filtration ; the 
substance remaining in the mother-liquor is then obtained in 
crystals by further cooling or concentrating ; the two crops of 
crystals are afterwards separately redissolved, and the frac- 
tionation repeated until each substance is obtained in a pure 
state, as shown by a determination of its melting-point 
(p. 13). 

Animal charcoal, prepared by strongly heating bones or blood 
out of contact with air, is often used in purifying organic com- 
pounds, as it has the property of absorbing from solutions coloured 
or resinous impurities. For this purpose the impure substance is 
dissolved in some suitable solvent, a small quantity of animal 
charcoal added, and the mixture heated for some time (with reflux 
condenser, p. 190) ; on subsequently filtering, a colourless or much 
lighter-coloured solution is usually obtained, and the substance 
generally crystallises more readily on cooling or evaporating. 
Before use, the charcoal should be repeatedly extracted with 
boiling hydrochloric acid to remove calcium salts and other 
impurities, washed well, dried, and heated strongly in a crucible 
closed with a lid. 

Another method extensively used in the separation and 
purification of organic substances, both solid arid liquid, is 
distillation in a current of steam. The substance and a 
little water are placed in a flask (A, fig. 2) which is connected 
with a condenser, and heated on a water- or sand-bath ; a rapid 
current of steam, generated in a separate vessel (B), is then 
passed through the mixture. The distillate, which contains 
the volatile organic substance in solution, or in suspension, is 
afterwards extracted with ether, or filtered, or treated in some 
other way according to circumstances. In this simple manner 
it is often possible to isolate a compound when all other 



8 



COMPOSITION, PURIFICATION, AND ANALYSIS 



methods fail ; it is, however, only applicable in the case of 
the comparatively few organic substances which are volatile 
in steam. Some compounds which cannot be distilled in the 
ordinary way because they undergo decomposition are volatile 
in steam, and pass over unchanged, even when their boiling- 
points are much higher than that of water. 







Fig. 2. 



When a substance volatilises very slowly, superheated steam is 
often employed ; in such cases the steam from B is passed through 
a heated coil of copper tubing before being led into A. 

Organic substances which boil without decomposing can 
be purified by distillation. The substance is placed in a 
distilling flask (A, fig. 3), which is connected with a con- 
denser, the neck of the flask being closed with a cork, through 
which a thermometer passes ; the bulb of the thermometer is 
placed just below the opening of the side-tube (B), and a few 
scraps of unglazed porcelain, or platinum, are put in the dis- 
tilling flask, to prevent * bumping ' or sudden ebullition. In 
the case of liquids which boil at temperatures above 130 or so, 



OF ORGANIC COMPOUNDS. 



9 



a long glass tube (C) without a water-jacket is used instead of 
a Liebig's condenser, which is apt to crack. If the compound 
to be purified contain only a small quantity of non-volatile 
impurities, the thermometer rises very rapidly as soon as the 
liquid begins to boil, but then remains practically stationary 
until almost the whole has distilled. Towards the end of the 




Fig. 3. 

operation, however, it begins to rise again, and distillation is 
then stopped, the impurities remaining in the distilling flask. 
If the distillate be now transferred to a clean flask, and 
redistilled, it will boil at a constant temperature, which is 
the boiling-point * of the liquid. 

All pure substances which boil without decomposing have 

a definite boiling-point (b.p.), which is dependent on the 

pressure. As the pressure diminishes, the boiling-point is 

lowered, so that, by carrying out the process under reduced 

* See foot-note, p. 14. 



10 COMPOSITION, PURIFICATION, AND ANALYSIS 

pressure, it is often possible to distil a substance which 
would undergo decomposition under ordinary atmospheric 
pressure, because in the latter case it would have to be 
heated more strongly. 

The boiling-point is one of the most important physical 
constants of a substance, and affords a valuable means of 
identifying it. An observation of the boiling-point should 
always be made with an apparatus similar to that shown 
(fig. 3), and a considerable quantity of the liquid should be 
distilled, in order to make sure that it has a constant boiling- 
point ; if not, it is impure, or it is decomposing. Before dis- 
tilling a substance, it should be carefully freed from any water 
it may contain ; in the case of liquids, this is done by shaking 
them with a few small pieces of fused calcium chloride, potas- 
sium carbonate, potash, or other dehydrating agent, according 
to circumstances, and then decanting or filtering. 

When a mixture of two (or more) volatile substances is 
distilled in the manner described above, the liquid begins to 
boil at some temperature lying between the boiling-points of 
its constituents. As distillation proceeds the boiling-point 
rises, and towards the end of the operation it usually becomes 
nearly the same as that of the liquid which boils at the 
higher temperature. In the case of a mixture of alcohol 
(b.p. 78-3) and water (b.p. 100), for example, the ther- 
mometer at "first registers some temperature between 78-3 
and 100 according to the proportion of the two substances, 
and the first portions of the distillate contain a larger pro- 
portion of alcohol than the original mixture. During dis- 
tillation the thermometer slowly and continuously rises, and 
at last registers 99-100, the portions passing over at this 
temperature consisting of practically pure water. The change 
in boiling-point is due to a change in the composition of the 
mixture; the alcohol, being more volatile, passes off more 
quickly than the water. It is possible, therefore, to partially 
separate a mixture of liquids by collecting the distillate in 
portions or fractions at intervals of 5 or 10, the operation 



OP ORGANIC COMPOUNDS. ll 

being termed fractional distillation. By redistilling each 
fraction separately a further separation is effected, and, after 
a sufficient number of operations, the constituents of the 
mixture are obtained in a practically pure condition, boiling 
at constant temperatures. Such a separation, however, can 
only be satisfactorily effected provided that there is a differ- 
ence of at least 20-30 between the boiling-points of the 
liquids ; in many cases, even when there is a greater difference 
than this, a complete separation cannot be accomplished. 

As an illustration of the process of fractional distillation, the case 
of a mixture of 50 c.c. of benzene (b.p. 81) and 50 c.c. of xylene 
(b.p. 140) may be taken. The mixture begins to boil at about 87, 
the thermometer rising gradually to 140 ; if the receiver be changed 
every 10, the following fractions are obtained, 

87-100 100-110 110-120 120-130 130-140 
33 c.c. 16 c.c. 8-5 c.c. 8 c.c. 33 c.c. 

(1) (2) (3) (4) (5) 

The first and last are larger than the others, bedause the tempera- 
tures at which they are collected are near the boiling-points 
of the constituents. If, now, the fractions 1 and 5 be sepa- 
rately redistilled, the former will yield a large fraction boiling at 
81-85, the latter giving one boiling at 135-140 ; other fractions, 
which are collected separately and added to 2, 3, or 4, being also 
obtained. By repeating these operations with the fractions 2, 3, 
and 4, a large proportion of the mixture is ultimately separated 
into two principal fractions, from which benzene and xylene 
respectively can be obtained in an almost pure condition by a 
final distillation. 

The process of fractional distillation is greatly facilitated by 
employing a flask with a long neck, or by causing the mixed 
vapours to pass through a long vertical tube before they 
enter the condenser. By this means the vapour of the 
liquid of higher boiling-point is partially condensed, and 
the liquid runs back into the distilling flask instead of 
passing over with the more volatile constituent. 

Fractional distillation is frequently carried out under 
reduced pressure for the reasons already stated in the case of 
ordinary distillation. A simple apparatus for this purpose is 



12 COMPOSITION, PURIFICATION, AND ANALYSIS 

easily made by inserting the side-tube of one distilling flask 
(A, fig. 4) into the neck of a second flask (B), and connecting 
the side-tube (of B) with a water-pump and pressure gauge.* 
The liquid to be distilled is placed in A ; the pump is then 
started, and, as soon as the pressure is sufficiently low, dis- 
tillation is carried out in the usual manner, the process being 
interrupted when the receiver is being changed, 



TO VACUUM PUMP AN 
PRESSURE GAUGE 




Fig. 4. 

Tests of Purity. Before attempting to determine the 
composition of an organic substance, its purity must be 
established. It would be useless to test for chlorine, for 
example, in an impure organic compound, since, even if 
a distinct indication were obtained, this element might be 
present (as a chloride) in the form of impurity. In the case 
of a compound, liquid or solid, which distils unchanged, a 

* Various forms of special apparatus are made for distillation under 
reduced pressure. 



OF ORGANIC COMPOUNDS. 



13 



determination of its boiling-point, or rather an examination 
of its behaviour on distillation, will show whether it is pure 
or not. A solid substance, however, is usually examined under 
the microscope, when the presence of impurity may often be 
detected, and an observation of its melting-point is always 
made. 

Pure substances which melt or liquefy without decom- 
posing do so at a definite temperature, which is called the 
melting-point of the- compound ; 
when, however, the substance 
is impure, not only is the 
melting-point usually lowered, 
but it is also rendered indefinite, 
the mixture becoming soft and 
pasty at a certain temperature, 
and not melting completely 
until heated considerably above 
this point. The determination 
of the melting-point affords, 
therefore, a valuable test of 
purity, and also serves as a 
means of identifying a com- 
pound. 

The apparatus generally em- 
ployed for determining the 
melting-point consists of a small 
beaker (a, fig. 5) of about 50 
c.c. capacity, containing con- 
centrated sulphuric acid, and 
fitted with a glass stirrer (b). 
A minute quantity of the 
substance is placed in a capillary tube (c), closed below, 
which is attached to a thermometer (d) by means of a 
small india-rubber ring, or simply caused to adhere to 
it by capillary attraction. The acid is slowly heated, 
being constantly stirred, and the temperature at which 




14 COMPOSITION, PURIFICATION, AND ANALYSIS 

the substance liquefies that is to say, its melting-point 
(m.p.) * is noted. 



QUALITATIVE ELEMENTARY ANALYSIS. 

A pure compound having been obtained, it is often possible, 
by noting its appearance, smell, crystalline form, solubility, 
and other properties, and by determining its melting- or 
boiling-point, to prove that it is identical with some substance 
the composition of which is known ; f when, however, this 
cannot be done, the next step is to ascertain of what elements 
the substance is composed. 

In order, in the first place, to make sure that the substance 
contains carbon that is to say, that it really is an organic 
compound a small quantity is heated on platinum foil. If 
it inflames and burns away, or swells up, giving a black mass, 
which on strongly heating entirely disappears, the substance 
is in all probability organic. The metallic salts of organic 
acids usually char when treated in this way, and on further 
heating, the carbonaceous matter burns away, leaving a residue 
which may be dissolved in water or acids and examined by 
the usual methods of inorganic analysis. Sodium acetate, 
for example, leaves sodium carbonate ; copper acetate, the 
oxide of the metal ; and silver acetate, metallic silver. If a 
halogen, sulphur, or phosphorus be present in the acid, 
it is generally found in the residue in combination with 
the metal. 

The behaviour of a substance when heated with concentrated 
sulphuric acid often affords an indication of the presence of 

* The observed melting- or boiling-point of a substance is usually rather 
lower than the true value, because, as a rule, a portion of the column of 
mercury is not immersed in the heating liquid or vapour. 

f The identity of two solids is best tested by mixing a small quantity of 
the substance under examination with an approximately equal quantity of 
the compound with which it is supposed to be identical, and then deter- 
mining the melting-point of the mixture ; if it be the same as that of 
the separate constituents, the identity of the latter may be taken to be 
established. 



OF ORGANIC COMPOUNDS. 15 

carbon, as many organic substances blacken under these 
conditions owing to the separation of carbonaceous matter. 

If neither of these tests give a decisive result, the compound 
is mixed with about ten times its weight of pure copper 
oxide, and the mixture heated to redness in a narrow tube of 
hard glass sealed at one end, the escaping gases being led into 
lime-water; under these conditions all organic substances* 
are decomposed, yielding carbon dioxide, the formation of 
which is proved by the lime-water becoming turbid. 

It is rarely necessary to test for hydrogen in organic 
compounds, and the only reliable method is to mix the dry 
substance with dry copper oxide and heat the mixture in a 
stream of dry air or oxygen (see pp. 18-20); if hydrogen be 
present, it will be oxidised to water, the formation of which 
may generally be seen, but which is more satisfactorily tested 
by passing the products of combustion through a weighed 
calcium chloride tube. 

The presence of nitrogen in an organic substance is fre- 
quently indicated by the peculiar, unpleasant smell, like that 
of burning feathers, which is observed on first heating the 
substance on platinum foil. A better test is to strongly heat 
a fairly large quantity of the substance with soda-lime f in a 
hard glass tube, when, if ammonia be evolved, the presence of 
nitrogen is proved. As, however, certain organic compounds 
containing nitrogen do not yield ammonia when heated with 
soda-lime, the following test must be applied before the 
absence of nitrogen may be considered as satisfactorily proved. 

A small quantity of the substance is placed in a narrow 
test tube, together with a bright piece of sodium (or potassium) 
about the size of a pea, and gently heated, care being taken, 
especially in the case of volatile compounds, that the metal 
is brought into contact with the substance and thoroughly 

* Except the stable carbonates and cyanides of the alkalies and alkaline 
earths. 

f Soda-lime is prepared by intimately mixing slaked lime and caustic 
soda, and strongly heating the mixture until it is quite dry. 



16 COMPOSITION, PURIFICATION, AND ANALYSIS 

chars it. The mixture is then heated more strongly, finally 
at a red heat, and after allowing to cool a little, the tube is 
broken by introducing the hot end into about 10 c.c. of water 
contained in an evaporating basin.* 

The alkaline solution is filtered from carbonaceous matter, 
a few drops of ferrous sulphate added to the filtrate, the 
mixture warmed for a short time, acidified with pure hydro- 
chloric acid, and tested with a drop of ferric chloride, when, 
if nitrogen were present in the original substance, a deep 
bluish-green colouration, or a precipitate of Prussian blue, 
is produced. 

This test depends on the fact that the nitrogen and some of 
the carbon in the organic compound combine with the sodium 
to form sodium cyanide ; when the alkaline solution of sodium 
cyanide is warmed with ferrous sulphate, ferrous hydrate is 
precipitated and sodium ferrocyanide is formed, 6NaCN + 
Fe(OH) 2 = Na 4 Fe(CN) G + 2;N T aOH, so that on afterwards 
adding a ferric salt f to the acidified solution, Prussian blue 
is produced. 

The presence of chlorine, bromine, or iodine in organic 
compounds cannot, as a rule, be detected by the methods 
employed in the examination of inorganic substances, as, for 
example, by means of silver nitrate, or by heating with man- 
ganese dioxide and sulphuric acid; chloroform, for instance, 
contains a very large proportion of chlorine, but when pure it 
gives no precipitate with silver nitrate, and simply boils away 
when heated with manganese dioxide and sulphuric acid. 

A simple test for the halogens is to take a piece of copper 
wire, and heat one end of it in the oxidising zone of the 
Bunsen flame until it ceases to colour the flame green. A 
small quantity of the substance is then heated on the end of 

* This should be done in such a way that the eyes are not 
endangered. 

f During the operation some of the ferrous hydrate generally becomes 
oxidised to ferric hydrate, which, on acidifying with hydrochloric acid, is 
converted into ferric chloride ; a precipitate of Prussian blue is thus at 
once produced. 



OF ORGANIC COMPOUNDS. 17 

the wire in the flame, when, if a halogen be present, a green 
colouration is usually observed, due to the formation of a 
volatile halogen compound of copper. As, however, this test 
sometimes fails, and as, moreover, it does not give any 
information as to which of the halogens is present, one of 
the following methods is generally adopted. 

(a) The substance is carefully heated with a bright piece 
of sodium or potassium exactly as described in testing for 
nitrogen. The alkaline solution is filtered from carbona- 
ceous matter, the filtrate acidified with pure nitric acid, 
and a portion tested with silver nitrate ; if a precipitate be 
formed, the presence of halogen (or of nitrogen, see below) 
in the original substance is proved, and its nature may be 
determined by submitting the rest of the solution, or the 
precipitate, to the usual examination. This test depends 
on the fact that when any organic substance containing 
chlorine, bromine, or iodine is heated with sodium, the 
halogen combines with the metal to form chloride, bromide, 
or iodide of sodium, which can then be tested for in the 
usual manner. 

(b) A small quantity of the substance is heated with pure 
lime in a tube of hard glass, as described later (p. 29). The 
mixture is allowed to cool, carefully shaken into distilled 
water, the solution acidified with nitric acid, filtered from 
carbonaceous matter, and tested with silver nitrate. If the 
substance contained a halogen chlorine, for instance heat- 
ing it with calcium oxide causes the formation of calcium 
chloride. 

When nitrogen is present the tests (a) and (b) for halogens 
are not conclusive, as the precipitate may be only silver 
cyanide; under these circumstances, the precipitate is col- 
lected, dried, and ignited on a porcelain crucible lid, when 
the cyanide is decomposed leaving silver, whereas the haloid 
silver salt is merely fused. The residue is then covered with 
dilute nitric acid ; if it does not dissolve completely the, 
presence of halogen is. established. 

Org. B 



18 COMPOSITION, PURIFICATION, AND ANALYSIS 

Sulphur and phosphorus may be detected by gradually 
adding the substance, in small quantities, to a fused mixture 
of potassium carbonate and nitre, heated on a piece of platinum 
foil; under these conditions the sulphur is oxidised to sul- 
phuric acid, the phosphorus to phosphoric acid. The residue 
is dissolved in water, and the solution of potassium salts 
tested for the above-mentioned acids in the usual way. 
Another method, similar in principle, consists in oxidising 
the substance with nitric acid in a sealed tube, as described 
later (p. 29). 

Sulphur may also be detected by heating the substance 
with sodium or potassium in the manner described above, 
and bringing a portion of the alkaline solution into contact 
with a bright silver coin ; if the original substance contained 
sulphur, an alkaline sulphide will have been produced, the 
presence of which will be at once recognised by the formation 
of a black stain on the silver coin. 

QUANTITATIVE ELEMENTARY ANALYSIS.* 

When the qualitative examination has been completed, the 
quantitative analysis may be proceeded with, but not before : 
the reason of this is, that the presence of certain elements 
necessitates a slight change in the methods to be employed, as 
will be shown below. 

Estimation of Carbon and Hydrogen. All organic com- 
pounds f are decomposed when brought into contact with red- 
hot copper oxide, the carbon being converted into carbon 
dioxide, the hydrogen into water ; by employing a known 
weight of substance, and collecting and weighing 1 these 
products of combustion, the percentage of carbon and 
hydrogen may be readily determined. The apparatus gener- 

* The following account of the methods most commonly adopted in the 
quantitative analysis of organic compounds is only intended to indicate the 
nature of the processes ; the details of manipulation, upon which success 
depends, can only he learned by practice in the laboratory. 

f With the exceptions already mentioned in the foot-note, p. 15. 



OF ORGANIC COMPOUNDS. 19 

ally used for this purpose is shown in the accompanying 
figures. 

The calcium chloride or water tube (fig. 6) is filled with 
granulated anhydrous calcium chloride, or with fragments of 
pumice moistened with concentrated sulphuric acid, and serves 
to ahsorb the water ; the potash bulbs (fig. 7) are partly filled, 
as shown, with strong potash (sp. gr. about 1-28), the small 
tube (a), which contains anhydrous calcium chloride, serving 




Fig. 6. Fig. 7. 

to retain the aqueous vapour which is taken up by the gases in 
their passage through the potash. The calcium chloride tube 
and the potash bulbs are carefully weighed before and after 
the combustion, the caps (b, I) with which they are closed 
being removed on both occasions ; the gain in weight of the 
former corresponds with the amount of water produced, that 
of the latter representing the amount of carbon dioxide 
formed. 

The combustion is carried out in a piece of hard glass com- 
bustion tube (a, b, fig. 8), which is usually about 90 cm. long, 
and open at both ends ; part of the tube (/to/) is filled with 
a layer of granulated copper oxide kept in its place by loose 
asbestos plugs (e, e). Before commencing the analysis the 
tube is heated in a combustion furnace (If), at a dull red heat, 
a current of air, carefully freed from carbon dioxide nnd mois- 
ture by passing first through potash contained in the wash- 
bottle (g\ and then through the two towers (h, j) * containing 

* In practice, two such sets of drying apparatus are usually employed, 
one for the air, the other for the oxygen. 



20 



COMPOSITION, PURIFICATION, AND ANALYSIS 



pumice 



moistened with concentrated sulphuric acid being 
led through it in order 
that any moisture or traces 
of organic matter may be 
removed ; the empty section 
only of the tube is then 
allowed to cool. 

The water tube (I) having 
been fitted into the end (b) 
through an india-rubber cork, 
and the potash bulbs (m) 
attached by means of a short 
piece of india-rubber tubing, 
0-15 to 0-2 gram of the sub- 
stance, accurately weighed 
out in a narrow porcelain 
or platinum boat (d), is in- 
troduced into the tube ; a 
roll of platinum foil (c) is 
then placed behind the boat 
in order to prevent as far 
as possible any backward 
diffusion of the products of 
combustion. When a very 
volatile liquid is to be 
analysed, the substance is 
weighed out in a thin glass 
bulb (shown on a larger scale 
at ri), which is afterwards 
placed in the boat (at d). 

A slow stream of air care- 
fully freed from moisture and 
carbon dioxide, as before, is 

fy now passed through the tube, 

the combustion of the sub- 
stance being started and regulated by turning on the gas 




OP ORGANIC COMPOUNDS. 21 

taps (beginning at c). As soon as the whole of the tube 
has been gradually raised to a dull red heat, the current 
of air is turned off, and a stream of pure oxygen is 
passed, in order to burn any remaining organic matter, 
and to oxidise the copper which has been formed by the 
reduction of some of the copper oxide; finally, air is again 
passed until the oxygen is expelled from the apparatus. 
The whole operation occupies from 1J to 3 hours, according 
to the nature of the substance. The water tube and the 
potash bulbs are then disconnected, their ends closed with 
the india-rubber caps, and allowed to stand for about two 
hours to cool thoroughly, when they are again weighed. 

Now, since the gain in weight of the potash bulbs is due 
to the absorption of carbon dioxide, which has been formed 
during the combustion, Jf-ths or y 3 T ths (C/C0 2 ) of this gain 
in weight represents the quantity of carbon in the amount of 
substance taken ; as also the gain in weight of the water 
tube corresponds with the amount of water formed, T 2 ^ths 
or -g-th (H 2 /H 2 0) of this increase represents the amount of 
hydrogen.* The percentage of carbon and hydrogen may 
therefore be calculated. 

Example. 0-1582 gram of substance gave on combustion 
0-0614 gram of H 2 and 0-3620 gram of C0 2 ; therefore, 
0-1582 gram of substance contains 0-0614 x 1/9 = 0-0068 gram 
of hydrogen, and 0-3620x3/11 = 0-0987 gram of carbon, 

so that 100 parts of the substance contain = 

U- LDoZ 

, 0-0987 x 100 co . , 

4-31 parts oi hydrogen, and IKQQ = 62-40 parts 01 

carbon. 

If the substance consist of carbon, hydrogen, and oxygen 
only, the difference between the sum of the above numbers 
and 100 must represent the quantity of oxygen; the per- 
centage composition of the substance is therefore, 

* The approximate atomic weights H=l, 0=12, O=16, N=14 are used 
here and in other calculations. 



22 COMPOSITION, PURIFICATION, AND ANALYSIS 

C 62-40 per cent. 

H 4-31 

33-29 ,. (by difference). 

The percentage of oxygen is always obtained by difference, 
there being no satisfactory method by which this element 
may be directly estimated. 

The following points remain to be noticed in connection 
with the determination of carbon and hydrogen. If the 
substance contain nitrogen, it is necessary to insert a roll of 
bright copper gauze, about four inches long, into the front 
part (&) of the tube in the place of some of the copper 
oxide ; this is kept red hot during the combustion, and 
serves to decompose any oxides of nitrogen* produced 
during the operation, which would otherwise be absorbed 
by the water in the calcium chloride tube and by the 
potash, and thus lead to erroneous results. When the sub- 
stance contains a halogen, a roll of silver gauze must be 
used in order to prevent any halogen or halogen compound 
of copper from passing into the absorption apparatus ; usually, 
in u analysing a substance containing halogens, sulphur, or 
phosphorus, the space / to / (fig. 8) is filled with lumps of 
fused lead chromate instead of copper oxide. Lead chromate, 
like copper oxide, is a powerful oxidising agent at high 
temperatures, its action being probably represented by the 
equation, 

4PbCr0 4 = 4Pb + 2Cr 2 3 + 10 0. 

Any sulphur dioxide, phosphorus pentoxide, or halogen pro- 
duced during the combustion is completely retained by the 
lead, as PbS0 4 , PbCl 2 , &c., and thus its passage into the 
absorption apparatus is prevented. 

* In order to render the roll of gauze as efficient as possible, it is 
heated in a blowpipe flame until thoroughly oxidised, and, while red 
hot, dropped into a little (1 c.c.) pure methyl alcohol contained in a 
test tube ; the methyl alcohol reduces the copper oxide, giving a very 
bright surface of copper. The roll is then completely freed from methyl 
alcohol by heating at 160-180 for half-an-hour, just before commencing 
the combustion. 



OF ORGANIC COMPOUNDS. 23 

Quantitative Determination of Nitrogen. Nitrogen may 
be estimated in three ways ; as nitrogen by Dumas' method, 
or as ammonia by Will and Yarren trap's, or by Kjeldahl's, 
method. 

1. Dumas' Method. This process is based on the fact that, 
when ignited with copper oxide, nitrogenous organic sub- 
stances are entirely decomposed into carbon dioxide, water, 
and nitrogen (or its oxides). If the gaseous products of com- 
bustion be passed over heated copper to decompose the oxides 
of nitrogen and then collected over potash, the carbon dioxide 
is absorbed, and the residual gas consists of practically pure 
nitrogen ; by measuring the volume of the gas obtained from 
a known weight of substance, the percentage of nitrogen can 
be readily ascertained. 

The analysis is carried out in a combustion tube similar to 
that used in the determination of carbon and hydrogen (fig. 8), 
but containing in the front end (b) a roll of copper gauze (see 
foot-note, p. 22). Instead, however, of placing the substance 
in a boat, the weighed quantity is intimately mixed with 
finely powdered copper oxide, this mixture occupying the 
space c to e. Before commencing to heat the substance, a 
stream of carbon dioxide* is passed through the tube until the 
air has been expelled, which is the case when the bubbles are 
almost entirely absorbed f in passing through the potash ; at 
the same time the roll of copper gauze and the front part of 
the tube are raised to dull redness. The stream of gas is now 
stopped and the combustion started by gradually heating the 
mixture of substance and copper oxide, the escaping gases 
being either collected over mercury in a eudiometer con- 
taining potash, or more conveniently in the apparatus shown 
in fig. 9. 

As soon as the whole of the tube has been raised to a dull- 



* The gas is generated in a Kipp's apparatus or by heating native 
magnesite. 

f The bubbles are never completely absorbed, as it is impossible to drive 
out the last traces of air. 



COMPOSITION, PURIFICATION, AND ANALYSIS 



or cherry-red heat, and gases cease to be evolved, a current of 
carbon dioxide is again led through the combustion tube until 
the rest of the nitrogen has been expelled. The eudiometer 
is then closed with the thumb, inverted in a cylinder of 

water, and the thumb re- 
moved so that the mercury 
may fall out and the strong 
potash mix with the water. 
After about half-an-hour'a 
time, the tube is held ver- 
tically in such a position 
that the levels of the water 
inside and outside are the 
same, and the volume (v) of 
the nitrogen is observed, the 
temperature (t) of the gas 
that is, of the water sur- 
rounding the tube and the 
height (B) of the barometer 
being also noted. 

The apparatus (Schiffs 
nitrometer) shown in fig. 9, 
which is now very generally 
used in nitrogen determina- 
Fig 9 tions, consists of a graduated 

tube (ac\ provided with a 

stop-cock (a) and a reservoir (d), by means of which the 
tube may be filled with potash (sp. gr. L3), and which also 1 
serves for regulating the pressure in the apparatus; the 
lower part of the tube (eb) is filled with mercury, which 
forms a seal and prevents the passage of the potash into- 
the combustion tube (e). After carbon dioxide has been 
passed through the combustion tube for a considerable' 
time, the tube (b) is connected, and the reservoir (dj 
lowered. If the bubbles are almost completely absorbed' 
as they ascend through the potash, the combustion is 




OF ORGANIC COMPOUNDS. 25 

ceeded with, the nitrogen remaining in the tube at the 
end of the operation being swept into the apparatus by 
means of carbon dioxide, as described above. The apparatus 
is now placed aside for about an hour to cool ; the reservoir 
(d) is then raised until the potash is at the same level in it 
and in the tube (ac), and the volume of nitrogen (v) is read 
off, the temperature (f) and the barometric pressure (B) 
being noted. 

The weight of nitrogen in the quantity of substance taken 
is readily ascertained when its volume (in cubic centimetres) 
has been determined by either of the methods described. 
Since the volume v is measured at t under a pressure B - w, 
where w = the tension of aqueous vapour in mm. of mer- 
cury* at the temperature t, the volume V at and 760 

B-W 273 
mm. would be v x -- x - As, now, 1 c.c. of 



nitrogen weighs 0-001251 gram at N.T.P.,f the weight of 
V c.c. will be V x 0-001251 gram. 

Example. 0-2248 gram of substance gave 7-1 c.c. of nitro- 
gen measured at 16; B = 753-5 mm., 0=13-5 mm. The 



weight of the gas, therefore, is 7-1 x x x 0-001251 



40 273 

89 



= 0-00808 gram, and the percentage of nitrogen 

= 3-59. 

2. Will and Varrentrap's Method depends on the fact 
already stated, that many nitrogenous organic substances, 
when heated with caustic alkalies, are decomposed in such a 

* Some of the values of w which are most frequently required are the 
following : 

t= 10 12 14 16 18" 20 

w= 9-14 10-43 11-88 13-51 15-33 17-36 mm. 
When the apparatus shown in fig. 9 is employed, the vapour tension of the 
strong potash is much less than that of pure water ; if the potash has 
a sp. gr. =1-3 it is usual, in practice, to deduct from B half the tension of 
aqueous vapour at the temperature t. 
f* Normal temperature and pressure. 



26 COMPOSITION, PURIFICATION, AND ANALYSIS 

way that the whole of their nitrogen is converted into 
ammonia; by estimating the ammonia produced by the 
decomposition of a known weight of the substance, the per- 
centage of nitrogen is determined. 

The apparatus (fig. 10) employed for this purpose consists 
of a piece of hard glass tube (ad) about 45 cm. long, 
drawn out and sealed at one end (a) ; an asbestos wad is 
loosely fitted into the end (a), and the space a to & is filled 
with coarsely powdered, freshly ignited soda-lime ; the part b 




Fig. 10. 

to c contains an intimate mixture of the weighed substance 
and finely powdered soda-lime, the remainder of the tube 
(c to d) being filled with coarsely powdered soda-lime only, 
the whole being kept in position by an asbestos wad (at d). 

The absorption apparatus (e) contains dilute hydrochloric 
acid, and serves to absorb the ammonia ; it is fitted into the 
open end of the tube by means of an india-rubber stopper. 
After tapping gently so as to ensure a clear channel for the 
escape of the gaseous products,* the tube is gradually heated 
in a combustion furnace, as in determining nitrogen volu- 
metrically (commencing at d), and when the whole has been 
raised to a red heat, the ammonia remaining in the tube is 
drawn into the absorption bulb by breaking off the sealed 
end and aspirating air through the apparatus. 

The amount of ammonia which has been produced may 
be determined gravimetrically by precipitation with platinic 
chloride, but, as a rule, a known volume of standard hydro- 

* Should this precaution be neglected the tube may get choked up and a 
serious explosion ensue. 



OP ORGANIC COMPOUNDS. 27 

chloric acid is introduced into the bulbs to start with, and 
the quantity neutralised by the ammonia is estimated volu- 
metrically by titration with standard alkali. 

The soda-lime method is not altogether satisfactory, because, 
owing to the decomposition of some of the ammonia formed during 
the operation, the results are usually too low. This decomposition 
may, to some extent, he prevented by adding a little sugar to the 
mixture of the substance and soda-lime. Furthermore, the method 
is not of universal application, as many nitrogenous organic sub- 
stances, especially those belonging to the aromatic group, do not 
yield the whole of their nitrogen in the form of ammonia when 
heated with soda-lime. 

3. Kjeldahl's Method, which is used more particularly in 
agricultural laboratories for the analysis of foods, fertilisers, 
&c., depends on the fact that when nitrogenous organic com- 
pounds are completely decomposed with hot, concentrated 
sulphuric acid, their nitrogen is obtained in the form of 
ammonium sulphate. 

The substance (0-5-5 grams) is placed in a round-bottomed 
flask of hard glass, and covered with about 20 c.c. of concen- 
trated sulphuric acid. The flask is then heated directly over 
an Argand burner, very gently at first, afterwards sufficiently 
to boil the acid, the process being continued until the liquid 
(which is usually very dark in colour owing to the separation 
of carbonaceous matter) has become almost colourless; as a 
rule, this operation is hastened by adding potassium sulphate 
(5-10 grams) after the first 15-30 minutes' heating, in order 
to raise the boiling-point. The ammonia which has been 
produced is separated by distilling with excess of caustic soda 
in a current of steam,* collected in standard sulphuric acid 
and estimated by titration. 

Quantitative Determination of Chlorine, Bromine, and 
Iodine. The halogens in an organic compound are very 
readily estimated by the method devised by Carius, which 
consists in oxidising the substance with nitric acid at a high 

* Special distillation apparatus is employed where this method is in 
frequent use. 



28 



COMPOSITION, PURIFICATION, AND ANALYSIS 



temperature in presence of silver nitrate. Under these con- 
ditions the carbon is completely oxidised to carbon dioxide, 
and the hydrogen to water, the halogen combining with the 
silver; the chloride, bromide, or iodide of silver thus pro- 
duced is collected and weighed in the ordinary way. The de- 
composition is carried out in a strong glass tube (ab, fig. 11), 
about 40 cm. long and 25 mm. wide, sealed at one end (a) ; 
the substance is weighed out in a small glass tube, which 
is placed in the larger tube together with a few crystals of 
silver nitrate. Pure concentrated nitric acid (about 10 c.c.) 




Fig. 11. 

having been added, the open end is drawn out and sealed, as 
shown at 5. The tube is then placed in an iron case, and 
heated in a specially constructed apparatus (fig. 11) at a 
temperature necessary to ensure complete decomposition, 
usually at about 180, for four hours; in the case of very 
stable substances, a much higher temperature and prolonged 
heating are required, and fuming nitric acid must be used. 
When quite cold the tube is opened,* the contents are 

* Very great care must always be taken in working with sealed tubes, as 
they frequently explode, and very serious accidents may occur. The tube 
should not be removed from its iron case, but should be cautiously pulled or 
tipped forward until the capillary just projects, using a cloth to protect the 



OP ORGANIC COMPOUNDS. 29 

transferred to a beaker with the aid of distilled water, and 
after boiling gently for about fifteen minutes the halogen 
silver salt is further treated in the usual way. 

Another method of estimating the halogens, especially useful 
in the case of substances which are difficult to decompose, 
consists in heating the compound with pure, freshly ignited 
quicklime (prepared by calcining marble) in a narrow piece 
of combustion tube, about 50 cm. long, and closed at one end. 
In charging the tube a little lime is first introduced, and then 
the mixture of the substance with about ten times its weight 
of quicklime, the remainder of the tube being nearly filled 
with quicklime. After tapping gently to form a clear channel 
for the passage of the gases (compare foot-note, p. 26), the 
tube is heated in a combustion furnace, the front part being 
raised to a bright red heat before the decomposition of the 
substance is proceeded with. When quite cold, the contents 
of the tube are cautiously shaken into excess of dilute nitric 
acid, the acid solution filtered from carbonaceous matter, and 
the halogen precipitated by the addition of silver nitrate. 

Sulphur and Phosphorus may be estimated by heating the 
substance in a sealed tube with nitric acid, as described above, 
but without the addition of silver nitrate. The whole of the 
sulphur is oxidised to sulphuric acid, the phosphorus to phos- 
phoric acid, which may then be estimated by the ordinary 
methods of analysis. 

Another method for determining sulphur and phosphorus, 
and also halogens (applicable only in the case of organic 
acids and some non-volatile neutral compounds), consists in 
heating the substance with a mixture of potassium carbonate 
and nitre in a platinum crucible, until the product is colourless. 
Here, again, the substance is completely oxidised, and the sul- 
phate or phosphate produced may be estimated in the residue. 

hand ; a Bunsen flame is then played cautiously on the tip of the capillary 
until the glass softens and blows out ; after the pressure has been released 
the tube is cut with a file in the usual way, but before doing so, the capil- 
lary should be examined in order to make sure that it has not been choked 
up by any solid particles. 



30 DEDUCTION OF A FORMULA. 



CHAPTER II. 

DEDUCTION OF A FORMULA FROM THE RESULTS OF ANALYSIS 
AND DETERMINATION OF MOLECULAR WEIGHT. 

The quantitative analysis of an organic compound is usually 
made with one of two objects : either to prove that a par- 
ticular compound is what it is supposed to be, or to ascertain 
the percentage composition of some pure substance, the nature 
of which is quite unknown. 

In the first case, the results of the analysis are compared 
with the calculated percentage composition, and if the two 
series of values agree within the limits of experimental error, 
the fact is taken as evidence that the substance in question is 
what it is believed to be. 

Example. A substance obtained by oxidising a fat with 
nitric acid is suspected to be succinic acid, C 4 H 6 4 , and, on 
analysis, it gave the following results: = 40-56, H = 5-12, 
= 54-32 (by difference) per cent. Since the percentage 
composition of succinic acid, calculated from its formula, 
is = 40-68, H = 5-08, = 54-24 per cent., the analysis 
aifords strong confirmation of the conclusion previously 
arrived at. 

In the second case, the nature of the substance being 
entirely unknown, it is necessary to deduce a formula from 
the analytical results that is to say, to find the relative 
numbers of the atoms in the molecule of the compound. 

Example. The percentage composition of a substance is 
found to be = 84-0, 11=16-0; deduce its formula. Since 
an atom of carbon weighs twelve times as much as an atom 
of hydrogen, the ratio between the number of atoms of 
carbon and the number of atoms of hydrogen is 84/12 : 16/1 
or 7 : 16 ; the formula CyH 16 may therefore be given to the 
substance, this formula having been obtained by dividing 



DEDUCTION OF A FORMULA. 31 

the percentage of each element by the atomic weight of that 
element. 

Example. The percentage composition of a substance is 
= 39-95, H = 6-69, = 53-36; deduce its formula. Pro- 
ceeding as before, the ratio between the number of atoms is 
found to be 3-33 : 6-69 : 3-33, 

39-95 6-69 53-36 

L> = = 6-66, 11 = : = o-by, U = _>, = o-oo ; 

dividing now each term by 3-33 to simplify, and allowing 
for experimental errors, the ratio of the atoms C : H : O 
= 1:2:1; the formula obtained in this way is therefore 
CH 2 0. 

In order, then, to calculate a formula from the percentage 
composition, the quantity of each element is divided by the 
atomic weight of that element, and the ratio is then expressed 
in whole numbers by dividing each term by the smallest, or 
by some simple fraction of the smallest term. 

Example. The percentage composition of a substance as 
determined by analysis is = 19-88, H = 6-88, N = 46-86, 
= 26-38 ; deduce its formula. 

= 1 = 1.657-1. 649 = 1 



H= 6 ' 88 =6-880-1.649 = 



14 

? = l-649- 1-649 = 1 



The formula, therefore, is CH 4 N 2 ; the ratio of the atoms 
determined experimentally is, of course, not exactly 1:4:2:1, 
owing to unavoidable errors, and for this reason, when a 
formula has been deduced in this way it should always be 
checked by calculating the percentage composition from the 
formula and comparing it with that found experimentally ; 
the two values for each element should agree within about 



32 DEDUCTION OF A FORMULA. 

0-1-0-3, the calculated value for carbon being usually a little 
higher, that for hydrogen a little lower, than the experimental 
value. 

The formula calculated from the results of analysis is the 
simplest expression of the ratio of the atoms, and is termed 
the empirical formula ; such a formula may, or may not, show 
how many atoms of each element the molecule of the sub- 
stance contains : formaldehyde, CH 2 ; acetic acid, C 2 H 4 2 ; 
and lactic acid, C 3 H 6 3 , for example, have the same per- 
centage composition, and would all be found, on analysis, to 
have the same empirical formula, CH 2 0. 

Determination of Molecular Weight. 

Further investigation is necessary in order to determine 
the molecular formula of a compound, by which is meant a 
formula expressing not only the ratio, but also the actual 
numbers of the atoms in the molecule ; in other words, the 
molecular weight of the compound must be determined. If, 
for example, it can be proved that a compound of the 
empirical formula CH 2 has a molecular weight = 60, its 
molecular formula must be C 2 H 4 2 (C 2 = 24, H 4 = 4, 2 = 32; 
total 60), and not CH 2 or C 3 H 6 3 ; that is to say, the 
molecule consists of two atoms of carbon, four of hydrogen, 
and two of oxygen. 

The determination of the molecular weight of a substance 
is therefore of great importance, and for this purpose certain 
physical methods, described later, are adopted whenever 
possible ; no purely chemical methods are known by which 
the molecular weight can be established with certainty, 
but such methods may often afford valuable indications, as 
will be seen from the following examples. 

Chemical Methods. In the case of organic acids, the 
analysis of a salt of the acid is often of value ; the silver salt 
is generally employed for this purpose, a weighed quantity 
being ignited in a porcelain crucible, when complete decom- 
position ensues, and a residue of pure silver is obtained. 



DEDUCTION OP A FORMULA. 33 

Example. The percentage composition of an organic acid 
is = 39-95, H = 6-69, = 53-36; its empirical formula is 
therefore CH 2 0. Its silver salt was prepared; 0-2960 gram 
of the pure salt gave on ignition 0-1620 gram of silver, so that 

,, . 0-1620 x 100 K . , 

the percentage of silver in the salt is rToTT^Ti = 54-73. 

U- 



Now, since 54-73 parts of silver are contained in 100 
parts of the salt, 107-7 parts of silver will be contained in 

10Q *Io 7 ' 7 = 196-78 P arts of salt ; but 107 - 7 is the atomic 

o4-7o 

weight of silver, so that if one molecule of the salt contain 
one atom of silver, its molecular weight must be 196-78, and, 
as the salt is formed from the acid by displacing 1 part of 
hydrogen by 107-7 parts of silver, the molecular weight of the 
acid must be 196-78-107-7 + 1 = 90-08. Since, however, 
the acid is composed of carbon, hydrogen, and oxygen, the 
atomic weights of which are all taken as whole numbers, the 
molecular weight of the acid may also be taken to be a whole 
number that is to say, 90 the value found experimentally 
being not quite correct, owing to errors in the analysis. The 
molecular weight of the acid being 90, its molecular formula 
is not CH 2 ( = 30) or C 2 H 4 2 ( = 60), but C 3 H 6 3 ( = 90), 
that of the silver salt being C 3 H 5 3 Ag ( = 196-7). 

This conclusion is based on the assumption that one mole- 
cule of the silver salt contains only one atom of silver that 
is to say, that the acid is monobasic ; until this assumption is 
proved to be correct, the analysis of the silver salt does not 
establish the molecular formula of the acid. If the acid had 
the molecular formula C 6 H 12 6 , and contained two atoms of 
displaceable hydrogen that is to say, were dibasic the silver 
salt C 6 H 10 6 Ag 2 would contain, as before, 54-75 per cent, of 
silver, and the molecular weight, calculated as above, would 
again appear to be 90. But if the acid were dibasic, it would 
probably be possible to displace only one atom of hydrogen, 
and obtain a hydrogen salt, C 6 H n 6 M', the analysis of which 
would point to the molecular formula C 6 H 12 6 . If this were 

Org. C 



34 DEDUCTION OF A FORMULA. 

found impossible, the fact might be taken as evidence against 
this molecular formula, and the conclusion might be drawn 
that the more probable molecular formula is C 3 H 6 3 . 

Most organic bases combine with hydrochloric acid to form 
salts which, like ammonium chloride, form double salts with 
platinic chloride and with auric chloride. These double salts 
usually have the composition B / 2 ,H 2 PtCl 6 , and B',HAuCl 4 , 
where B' represents one molecule of a monacid base, such as 
methylamine, CH 5 N, ethylamine, C^^N, &c. When these 
salts are ignited in a porcelain crucible, pure finely divided 
platinum, or gold, remains ; so that the percentage of metal 
in the salt is very easily determined. Assuming that one 
molecule of the salt contains one atom of platinum or gold, 
and that the salt has the above composition, the molecular 
weight of the base can be calculated. 

Example. The platinum double salt (platinicliloride) of 
an organic base gave on ignition 37-0 per cent, of platinum ; 
what is its probable molecular weight 1 Since 37-0 parts of 
platinum are contained in 100 parts of the salt, 195 parts of 

the metal are contained in ^=-^ = 527 parts of salt, and, 

as 195 is the atomic weight of platinum, the molecular 
weight of the salt is 527. The molecular weight of 

B 



., , tr * -r-r -.-TV . ., f , 9 ft 9fl 

the base (C 3 H 9 N) is therefore | or 

527 - (2 + 195 + 212-2) 527 - 409-2 

~2~ ~^~ ' y * 

As in the case of acids, so in that of bases, the molecular 
weight calculated from the analytical results may be wrong, 
because it is not known whether the compound is a monacid 
base or not. Some bases are diacid, and form platinichlorides 
of the composition B",H 2 PtCl 6 , so that a diacid base of tjtie 
molecular weight 118 would yield a platinichloride containing 
the same percentage of platinum as the salt of a monacid base 
of the molecular weight 59. 

It will be seen from the above examples that, assuming 



DEDUCTION OP A FORMULA. 35 

that there is only one atom of any particular element in the 
molecule of the compound, the probable molecular weight may 
be calculated from the results of any analysis which gives the 
percentage of that particular element. 

This being the case, the probable molecular formula of a 
compound may often be determined by preparing and analys- 
ing some simple derivative. 

Example. A liquid hydrocarbon has the percentage 
composition = 92-31, 11 = 7-69; its empirical formula is 
therefore CH. On treating this hydrocarbon with bromine, 
it yields hydrogen bromide and a bromo-derivative consisting 
of = 45-86, H = 3-18, Br = 50-96 per cent. The empirical 
formula of this derivative is, 






C = ^p = 3-82 -0.637 = 

o-io 

H = - = 3.18 4-0-637 = 
Br = -7^- = 0-637 - 0-637 = 



Now, since it is known from experience that, as a rule, the 
number of atoms of carbon in the molecule is not changed on 
treating with bromine, the probable molecular formula of the 
hydrocarbon is C 6 H 6 ; it cannot be less than this, but it may 
be greater. A hydrocarbon C 12 H 12 , for example, might give 
a bromo-derivative C 12 H 10 Br 2 , and these compounds would 
have the same percentage compositions as C 6 H 6 and C 6 H 5 Br 
respectively. 

The probable molecular weight may often be deduced with 
tolerable certainty by studying the physical properties of a 
substance. When, for example, acetone is distilled with con- 
centrated sulphuric acid, it is converted into a hydrocarbon 
which, on analysis, is found to have the empirical formula 
C 3 H 4 . The fact that this hydrocarbon boils at 163 affords 
very strong evidence that the molecular formula is not C 3 H 4 or 
C 6 H 8 , but probably C 9 H 12 , because other hydrocarbons which 
contain only three or six atoms of carbon in the molecule boil 



36 DEDUCTION OF A FORMULA. 

at temperatures much below 163, and an increase in molecular 
weight is generally accompanied by a rise in boiling-point. 

Physical Methods. One of the most important physical 
methods by which the molecular weight can be ascertained is 
by determining the vapour density. This method is based on 
the hypothesis that equal volumes of all gases measured 
under the same conditions of temperature and pressure 
contain the same number of molecules (Avogadro's Law). 
If, therefore, the weights of equal volumes of various gases 
be determined under the same conditions, these weights must 
be in the same proportion as the weights of the molecules of 
the gases. In order, then, to determine the molecular weight 
of a substance, it is necessary to find the weight of a given 
volume of the vapour of that substance; this is then com- 
pared with the weight of the same volume of hydrogen 
measured under the same conditions, the former divided by 
the latter giving the specific gravity or vapour density (V.D.) 
of the gas compared with hydrogen as unity. 

Now, since the vapour density is a number expressing how 
many times a given volume of the gas is heavier than the 
same volume of hydrogen, it also expresses how many times 
one molecule of the substance is heavier than one molecule 
of hydrogen ( = 2), because equal volumes contain an equal 
number of molecules. The molecular weight, on the other 
hand, is a number expressing how many times one molecule 
of the substance is heavier than one atom of hydrogen 
( = 1); therefore the molecular weight is double the vapour 
density, because the standard with which it is compared is 
half as great : M. W. = V.D. x 2. 

Sometimes air is taken as unit weight in stating the specific 
gravity or vapour density of a gas; since air is 1443 times 

heavier than hydrogen, the sp. gr. compared with air is 

of the value when compared with hydrogen ; so that, in order 
to obtain the molecular weight, the sp. gr. is in such cases 
multiplied by 28-86 = 2 x 14-43. 



DEDUCTION OP A FORMULA. 37 

Determination of Vapour Density. 

The vapour density of a substance is ascertained experi- 
mentally, (a) by measuring the volume occupied by the 
vapour of a known weight of the substance at known 
temperature and pressure, or (b) by ascertaining the weight 
of a known volume of the vapour of the substance at 
known temperature and pressure. The observed volume 
of the vapour is then reduced to and 760 mm., and 
the weight of a volume of hydrogen at and 760 mm. 
equal to the corrected volume of the vapour is calculated ; 
the weight of the vapour divided by that of the hydrogen 
is the vapour density. 

Example. An organic liquid has the empirical formula 
C 4 H 10 ; 0-062 gram of the liquid gave 23-2 c.c. of vapour 
at 50 and 720 mm., what is its molecular formula ? 

720 273 
The volume at and 760 = 23-2 x x 5Q =18-57 c.c. 



and 1 c.c. of hydrogen at KT.P. weighs 0-0(!)00899 gram ; 
therefore 18-57 c.c. weigh 0-00167 gram. 

The weight of the vapour 0-062 _ 371 _ y-p 

The weight of the hydrogen ~ 0-00167 ~ 
The molecular weight = V.D. x 2 or 37-1 x 2 = 74-2. 

Since the molecular weight of a compound of the empirical 
formula C 4 H 10 is calculated to be 74, the determination of 
the vapour density proves that the molecular formula of the 
liquid is C 4 H 10 0, so that in this case the empirical is iden- 
tical with the molecular formula. The molecular weight 
determined experimentally from the vapour density frequently 
differs from the theoretical value by several units, owing to 
experimental errors; this, however, is of little importance, 
since all that is required in most cases is to decide between 
multiples of the empirical formula ; in the above example, 
between C 4 H 10 = 74, C 8 H 20 2 = 148, &c. 

The determination of the vapour density is only possible 



38 



DEDUCTION OP A FORMULA. 



when a substance can be converted into vapour without 
decomposing under the conditions of the experiment. In 
many cases, however, a non-volatile compound, or a com- 
pound which cannot be vaporised without decomposing, can 
be converted into some simple derivative which is volatile, 
so that, by determining the vapour density of the latter, the 
j, molecular weight of the 

parent substance can be 
ascertained. 

The following are some 
of the methods employed 
in determining vapour den- 
sity. 

Gay-Lussac's or Hof- 
mann's Method. A gradu- 
ated barometer tube (ab, 
fig. 12), about 85 cm. long 
and 35 mm. wide, filled 
with and then inverted in 
mercury, is surrounded by 
a wider tube (c), through 
which the vapour of some 
liquid boiling at a known 
and constant temperature is 
passed. For this purpose 
the upper end of the outer 
tube (c) is connected with a 
vessel (A), usually made of 
copper, containing the heat- 
ing liquid, which is kept 
in rapid ebullition. The liquids most commonly employed 
are water (b.p. 100), xylene (b.p. 140), aniline (b.p. 
183), and ethyl benzoate (b.p. 213). The condensed liquid 
escapes through the side-tube (/), and is collected for sub- 
sequent use. 

As soon as the barometer tube is at a constant temperature, 




Fig. 12. 



DEDUCTION OF A FORMULA. 39 

a weighed quantity (about 0-05 gram) of the substance, con- 
tained in a small stoppered vessel (d\ which it fills completely, 
is placed under the open end (b). The vessel immediately 
rises to the surface of the mercury in the tube, the substance 
vaporises into the Torricellian vacuum, and the mercury is 
forced downwards ; as soon as the level remains stationary, 
the volume of the vapour is noted. The temperature of the 
vapour is the boiling-point of the liquid employed to heat 
the barometer tube. The pressure is determined by sub- 
tracting the height of the column of mercury in the inner 
tube (ab), above the level in the trough, from the height 
of the barometer, both readings having been first reduced 
to 0.* The weight of the vapour is that of the substance 
taken. 

The great advantage of this method lies in the fact that it 
affords a means of determining the vapour density of sub- 
stances under greatly reduced pressures, and therefore at 
temperatures very much below their ordinary boiling-points, 
so that it can often be employed with 
success in the case of substances which 
are only volatile without decomposing 
under reduced pressure. 

Dumas' Method. A globe-shaped 
vessel of about 200 c.c. capacity (a, 
fig. 13), the neck of which is drawn 
out to a fine tube, is carefully weighed, 
the temperature (tf) and barometric 
pressure (B') being noted. A fairly 
large quantity of the substance (about 
8-10 grams) is now introduced by Flg * 13 * 

gently heating the globe and quickly dipping the tube into 
the liquid. The vessel is then immersed in an oil-bath 
(shown in section in fig. 13) containing a thermometer (b) t 
and heated at a constant temperature, at least 20 above 
the boiling-point of the compound. The air in the apparatus 
* By correcting for the expansion of the mercury. 




40 



DEDUCTION OF A FORMULA. 



is quickly expelled by the rapid vaporisation of the sub- 
stance, and the vessel is filled with the vapour of the liquid. 
As soon as the whole of the liquid has been vaporised, 
which is known by the fact that gas ceases to issue 

from the fine tube, the 
point of the latter is 
sealed before the blow- 
pipe, the temperature of 
the oil-bath (t) and 
the height of the 
barometer (B) being 
noted. The globe is 
allowed to cool, and is 
then cleaned, dried, 
and weighed. 

The point of the tube 
is now broken under 
water (or mercury), 
which rushes in and 
fills the globe com- 
pletely, except for the 
minute quantity of 
liquid produced by the 
condensation of the 
vapour in the globe; 
the globe is again 
weighed, and its capacity 
Fig. 14. or volume (v) obtained 

from the weight of the 

water contained in it. The volume may also be measured 
directly by transferring the liquid from the globe to a 
graduated vessel. 

When the globe is weighed the first time it is full of air, 
but at the second weighing it is full of vapour ; if, therefore, 
the first weight be subtracted from the second, the difference, 
W, is the weight of the volume, v, of vapour less the weight 




DEDUCTION OP A FORMULA. 41 

of the volume, v, of air.* The weight of the air is calculated 
by reducing the volume, v, at t' and B' to N.T.P., and multi- 
plying by 0-001293, the weight of 1 c.c. of air at N.T.P. ; 
this weight added to W gives the weight of the volume, ?;, of 
vapour at t and B. The volume, v, of vapour at t and B is 
then reduced to N.T.P., the weight of an equal volume of 
hydrogen at N.T.P. calculated, and divided into the weight 
of the vapour. 

Victor Meyer's Method. Owing to its simplicity, and the 
rapidity with which the determination may be made, this 
method is now used whenever possible ; the apparatus is 
represented in fig. 14. The bulb tube (ab) is closed (at a) by 
means of an india-rubber stopper, and heated by the vapour 
of some constant boiling liquid f contained in the outer vessel 
(c) ; as the air expands it escapes through the narrow tube (d), 
which dips under the water in the vessel (e). As soon as the 
temperature of the bulb tube (ab) becomes constant that is 
to say, when bubbles of air cease to escape (from d) the 
graduated tube (g) is filled with water and inverted over the 
end of d ; the stopper (a) is now removed, and a small bottle 
or bulb (d, fig. 12) completely filled with a weighed quantity 
(about 0-05 gram) of the liquid dropped into the apparatus,! 
the stopper being replaced as quickly as possible. The sub- 
stance immediately vaporises, and the vapour forces some of 
the air out of the apparatus into the graduated vessel (g). 
When air ceases to issue (from d), the stopper (a) is at once 
taken out to prevent the water (in e) from being sucked back 
into the apparatus. 

The volume of the vapour is ascertained by measuring the 

* Changes in the temperature of the air, height of the barometer, and 
volume of the globe occurring during the experiment may be neglected. 

t See page 38 ; in determining the vapour density of substances of high 
boiling-point, diphenylamine (b.p. 310) or sulphur (b.p. 448) may be used, 
or the bulb tube (ab) may be heated at a constant temperature in a metal 
bath. 

J In order to prevent fracture, a little dry asbestos, glass-wool, or sand 
is placed in 6. 



42 DEDUCTION OP A FORMULA. 

volume (v) of the air in the graduated tube,* its temperature 
(t) and the barometric pressure (B) being noted. The volume 
of the air (in g) is not the same as that actually occupied by 
the hot vapour (in ab), because the displaced air has been 
cooled, and is measured under a different pressure. Its 
volume now is equal to that tvhich the given iveight of vapour 
would occupy under the same conditions of temperature and 
pressure. 

The temperature of the volume, v, of air being t, and the 
height of the barometer B, the volume at N.T.P. would be 

273 E-iv , . ,, 
V * 273 t * 760 * w ^ ein g *"* tension of aqueous vapour at 

t (see foot-note, p. 25). The weight of an equal volume of 
hydrogen at N.T.P. is then calculated and divided into the 
weight of the substance taken; the vapour density is thus 
obtained. 

The liquid in (c) should have a boiling-point at least 25 higher 
than that of the substance of which the vapour density is required 
in order that the latter may be rapidly vaporised otherwise its 
vapour may condense again higher up the tube. If, as is generally 
the case, the temperature of the air in the tube (ab) be lower at the 
top than at the bottom, this is of no consequence ; nor does it 
matter if the displaced air be colder than the vapour, or if the 
vapour be cooled a little while it is displacing the air. This is 
because any diminution in the volume of the air displaced from the 
tube (ab) arising from these causes is exactly compensated for 
during the subsequent cooling to t ; the lower the original tem- 
perature, the smaller the subsequent contraction. If, for example, 
the hot vapour measured 25 c.c. at 250, but only displaced 24-04 c.c. 
of air owing to the latter being of the average temperature of 230, 
the 24-04 c.c. of air at 230 would occupy the same volume as 25 c.c. 
at 250 if both were cooled to t. > 

Determination of Molecular Weight from the Depression of 
the Freezing-point. When sugar is dissolved in water, the 
solution has a lower freezing-point than that of pure water, 
and the extent to which the freezing-point is lowered or 

* Compare p. 24. 



DEDUCTION OF A FORMULA. 43 

depressed is, within certain limits of concentration, directly 
proportional to the weight of sugar in solution; 1 part of 
sugar, for example, dissolved in 100 parts of water depresses 
the freezing-point about 0-058 that is to say, the solution 
freezes at -0-058 instead of at 0, the freezing-point of pure 
water; 2 parts of sugar dissolved in 100 parts of water lower 
the freezing-point 0-116, 3 parts 0-174, and so on. 

Solutions of other organic compounds in other solvents, 
such as acetic acid, benzene, &c., behave in a similar manner, 
and, in sufficiently dilute solutions, the depression of the 
freezing-point is (approximately) proportional to the number 
of molecules of the dissolved substance in a given weight of 
the solvent, and independent of the nature of the substance. 
If, then, molecular proportions of various substances be 
separately dissolved in a given (and sufficiently large) quan- 
tity of the same solvent, the depression of the freezing-point 
is the same (approximately) in all the solutions, but different 
with different solvents. From actual experiments with dilute 
solutions, the depression of the freezing-point which should be 
produced by dissolving the molecular weight in grams of any 
substance in 1 00 grams of a given solvent can be calculated ; 
the constant quantity, K, which is thus found is termed the 
molecular depression of that solvent. 

If, for example, 1 gram of sugar dissolved in 100 grams of 
water depresses the freezing-point fyy 0-058, 342 grams (i.e. the 
molecular weight in grams) would theoretically cause a depression 
of 19-8 = K. 

This constant having been determined for any solvent, the 
molecular weight, M, of a substance can then be ascertained 
by observing the depression of the freezing-point of a suffi- 
ciently dilute solution, containing a known quantity of that 
substance. If 1 gram of the substance were dissolved in 100 
grams of the solvent, the observed depression, D, would be 

K x ^ because K is the depression produced by the molecular 
weight in grams that is to say, by M grams and the de- 



44 



DEDUCTION OF A FORMULA. 



pression varies directly with the weight of dissolved substance. 
If, again, P grams of the substance were dissolved in 100 

grams of the solvent, the de- 
p 

pression, D = K x ^, hence the 

KxP T;r 

molecular weight M = =r ; Jl 

and P being known, if the de- 
pression be ascertained experi- 
mentally, the molecular weight, 
M, can be calculated. 

This method of determining 
the molecular weight of organic 
compounds was first applied by 
Raoult, and is usually known 
as Raoult's or the cryoscopic 
method. The observation is 
made with the aid of the 
apparatus devised by Beckmann 
(fig. 15), in the following 
manner : A large tube (A), 
about 3 cm. in diameter, and 
provided with a side-tube (B), 
is closed with a cork (C), 
through which pass a stirrer (a) 
and a thermometer (b) graduated 
to T ^j-. A weighed quantity 
(about 25 grams) of the solvent 
is placed in the tube, which is 
then fitted into a wider tube 
(D), which serves as an air- 
jacket and prevents a too rapid 
change in temperature. The 
apparatus is now introduced 

through a hole in the metal plate (E) into a vessel which 
is partly filled with a liquid, the temperature of which 




Fig. 15. 



DEDUCTION OF A FORMULA. 45 

is about 5 lower than the freezing-point of the solvent. 
The solvent (in A) is now constantly stirred, when the 
thermometer rapidly falls, arid sinks below the freezing- 
point of the solvent, until the latter begins to freeze ; the 
thermometer now rises again, but soon becomes stationary 
at a temperature which is the freezing-point of the solvent. 
A weighed quantity of the substance is now introduced 
through the side-tube (B), and after first allowing the 
solvent to melt completely, the freezing-point of the solution 
is ascertained as before. The difference between the two 
freezing-points is the depression (D) ; the molecular weight of 
the substance is then calculated with the aid of the above 
formula. 

Example. 4-9818 grams of cane-sugar (C 12 H 22 O n ) dis- 
solved in 96-94 grams of water caused a depression in 
the freezing-point of 0-295 (D). Since 96-94 grams of 
the solvent contain 4-9818 grams of substance, P, the 
quantity in 100 grams = 5- 139 grams. The constant, K, 
for water is 19; hence the molecular weight, M, of cane- 

, 19x5-139 001 
sugar is found to be . = ool, the true value 

being 342. 

As in the determination of molecular weight from the 
vapour density, the experimental and theoretical values 
frequently differ by several units, but this is of little import- 
ance for the reasons already stated. 

The constants, K, for the solvents most frequently used 
are: acetic acid, 39; benzene, 49; water, 19. 

Determination of Molecular Weight from the Elevation of 
the Boiling-point. When molecular proportions of different 
substances are dissolved in a fixed and sufficiently large 
quantity of a given solvent, the boiling-point of the solution 
is raised by the same amount; experiments with dilute 
solutions give the actual rise in boiling-point, and then by 
calculation, the molecular elevation that is, the rise which 
should be produced by dissolving the molecular weight in 



46 DEDUCTION OF A FORMULA. 

grams of the substance in 100 grams of the solvent may "be 
deduced. 

The value thus determined is (approximately) a constant, 
K, but is different for different solvents ; if now the value of 
K is known, the molecular weight of a substance soluble in 
that solvent can be determined experimentally by finding the 
elevation of the boiling-point, E, produced by dissolving a 
known weight of the substance in a known weight of the 

solvent, the formula M = = being employed. (Compare 

p. 44.) 

One of the simplest forms of apparatus for determining 
molecular weights by this, the ebullioscopic method, is that 
devised by Landsberger (fig. 16). A suitable quantity of the 
solvent is placed in the tube (a), which is about 16 cm. in 
height and 3 cm. in diameter, and which has a small opening 
at (b) for the escape of vapour; this tube (a) is fitted by 
means of a cork into a larger one (c) which serves as an air- 
jacket, and the outlet (d) of which is connected with an 
ordinary Liebig's condenser. The inner tube (a) is closed 
with a cork through which pass a thermometer, graduated 
to ^o> an( * a tu ^ e ( e \ the end of which has been cut off in a 
slanting direction, or perforated with a number of holes. 
The solvent in the tube (a) is not heated directly, but only by 
the vapour of the same solvent that is generated in the flask 
(/) ; in this way superheating is avoided. 

The boiling-point of the solvent alone is first determined 
by heating the solvent in the flask (/) and passing its 
vapour through the solvent in (a) until the thermometer 
shows a constant temperature ; the solvent in (a) is then 
mixed with that in the flask (/), about the same quantity 
as originally used being poured back into the tube (a). A 
weighed quantity of the substance is now placed in (a), and 
vapour from (/) is again passed until the temperature is 
again constant. The difference between the two readings 
gives the elevation E. The weight of the solvent in (a) at 



DEDUCTION OP A FORMULA. 



47 



the time of the second reading has now to be found, and the 
molecular weight of the substance can then be calculated. 



: i 





m 



Fig. 16. 

Instead of determining the amount of solvent by direct weighing, 
the tube (a) may be graduated, as suggested by Walker, and the 
weight of the solvent ascertained with sufficient accuracy by 
multiplying its volume by its specific gravity at its boiling-point. 
The quantity of solvent originally placed in (a) should be so 
chosen that by the time the solvent is boiling constantly, the total 
quantity amounts to about 10 grams. 



48 DEDUCTION OF A FORMULA. 

Example. 0-5617 gram of naphthalene dissolved in carbon 
disulphide raised the boiling-point by 0-784; the solvent 
alone weighed 12-74 grams, hence 100 grams of the solvent 
would have contained 4-42 grams of substance. The constant, 
K, for carbon disulphide is 23-7 ; the calculated molecular 

weight, therefore, is /T = 134, the true value being 



128. The constants for the solvents generally used are : 
acetic acid, 25-3; benzene, 26-7; water, 5-2; ether, 21-1; 
ethyl alcohol, 11-5; acetone, 16-7. 

The cryoscopic and ebullioscopic methods are not applicable to 
all substances ; in the case of electrolytes the results obtained with 
certain solvents such as water, acetic acid, and alcohol accord with 
the view that the chemical molecules of the dissolved substance 
are dissociated into simpler portions (ions) ; in the case of some 
non-electrolytes the results obtained with solvents such as 
ether, benzene, and carbon disulphide indicate that the chemical 
molecules of the dissolved substance are associated, or form 
more complex aggregates. 



CHAPTEE III. 

CONSTITUTION OR STRUCTURE OF ORGANIC COMPOUNDS. 

Even when the molecular formula of an organic compound 
has been established by the methods described in the fore- 
going pages, the most difficult and important steps in the 
investigation of the substance have still to be taken. 

Many cases are known in which two or more compounds 
have the same molecular formula, and yet are different in 
chemical and physical properties ; there are, for example, 
two compounds of the molecular formula C 2 H 4 2 , three 
of the molecular formula C 5 H 12 , and so on. Now, if the 
properties of a compound depended simply on the nature 
and number of the atoms of which it is composed, there 



CONSTITUTION OF ORGANIC COMPOUNDS. 49 

could not be two or more different substances having the 
.same molecular formula. 

The only possible conclusion to be drawn from the proved 
(existence of such compounds is, therefore, that the difference 
ibetween them is a difference in constitution ; in other words, 
vthat the atoms of which their molecules are composed are 
(differently united. 

There is nothing at all improbable in this conclusion : in 
;the case of simple inorganic compounds, the behaviour of any 
^particular atom depends on the nature of the other atoms or 
; groups of atoms with which it is united. The hydrogen atoms 
jn ammonia, NH 3 , for example, are not, but the hydrogen atoms 
iin sulphuric acid, H 2 S0 4 , are displaceable by zinc, and the 
(Only difference between them is a difference in their state of 
(.combination. It is just the same in the case of organic com- 
ipounds; the state of combination determines the behaviour 
,of the atoms, and therefore the properties of the compound 
.depend on the state of combination of all the atoms of which 
its molecule is composed. 

Now, although the actual arrangement or structure of the 
molecule cannot be directly determined, it is possible to 
^obtain some idea of the state of combination of the atoms by 
studying the chemical behaviour of the compound. Methyl 
alcohol, CH 4 0, for example, is readily acted on by sodium, 
yielding a compound of the composition CH 3 NaO, which is 
formed by the displacement of one hydrogen atom (a) by one 
atom of the metal ; the other three hydrogen atoms in methyl 
alcohol cannot be displaced, no matter how large a quantity of 
sodium be employed. Again, when methyl alcohol is treated 
with hydrogen chloride under certain conditions, one atom of 
hydrogen and one atom of oxygen are displaced by one atom 
of chlorine, a compound of the composition CH 3 C1 being 
formed, 

CH 4 + HC1 = CH 3 C1 + H 2 0. 

When this compound is heated with water, it is transformed 
into methyl alcohol, one atom of chlorine being displaced by 

Org. D 



50 CONSTITUTION OF ORGANIC COMPOUNDS. 

one atom of oxygen and one atom of hydrogen ; the change 
is, in fact, the reverse of that represented above. 

From these and other experiments it is concluded that 
methyl alcohol contains one atom of hydrogen (a) combined 
differently from the other three ; also that one atom of hydrogen 
is closely associated with the oxygen atom, because the two 
are constantly displaced and replaced together ; as, further, 
the compound CH 3 C1 does not contain a hydrogen atom 
which can be displaced by sodium, it is concluded that the 
particular hydrogen atom (a) in methyl alcohol which is dis- 
placeable by sodium is the same as that which is closely 
associated with the oxygen atom. These conclusions may 
be expressed by the formula? CH 3 (OH) and CH 3 (ONa). 

Now, any compound, such as ethyl alcohol, C 2 H 6 0, propyl 
alcohol, C 3 H 8 0, &c., which behaves like methyl alcohol under 
the same conditions may be assumed to contain one atom 
of hydrogen and one atom of oxygen in the same state of 
combination as in methyl alcohol, and may be represented by 
formula such as C 2 H 5 (OH), C 3 H 7 (OH), &c. The constitution 
of any compound may be ascertained, therefore, by carefully 
studying its chemical behaviour under various conditions or 
by comparing its behaviour with that of some compound of 
known constitution. Atoms or groups of atoms which are 
found to show the same behaviour are considered to be 
in a similar state of combination. It is thus possible to 
determine the state of combination of many or of all the 
atoms of which the molecule is composed, and then, by using 
suitable formulae, not only the state of combination or con- 
stitution, but also the chemical behaviour, of the substance 
may be expressed. Formulae employed for this purpose are 
called rational or constitutional formulae. 

Another way of representing compounds is by means of 
graphic formulae, the object of which is to express still more 
fully and clearly the constitution and chemical behaviour of 
the substance. Before giving examples of the use of 
graphic formulae, it will be necessary to consider the molecular 



CONSTITUTION OF ORGANIC COMPOUNDS. 51 

formulae of some of the simpler organic compounds. For this 
purpose attention may be directed in the first place to com- 
pounds such as (a) CH 4 and CHC1 3 ; (6) C0 2 and COS ; 
(c) COC1 2 ; and (d) HCN, which contain only one atom of 
carbon in the molecule. In all these compounds the atom of 
carbon is combined with (a) 4 monovalent or monad atoms, 
(&) 2 dyad atoms, (c) 1 dyad and 2 monad atoms, or (d) 1 
triad and 1 monad atom that is to say, with four monad 
atoms or their valency equivalent. With the doubtful 
exception of carbon monoxide, CO,* no compound containing 
only one carbon atom is known, in which the carbon atom is 
combined with more or less than four monad elements or 
their valency equivalent; carbon, therefore, is tetravalent, 
and this fact may be expressed by writing its symbol, 

or =C= or C 



or in any other way, four lines being drawn simply to express 
its tetravalent character. 

For similar reasons the monovalent hydrogen atom may 
be represented by H , divalent oxygen by 0= or , 

trivalent nitrogen by N= or N" , and so on, the number 
of lines serving to recall the valency of the atom. 

If, now, in the case of substances such as CH 4 , CH 3 C1, 
CHC1 3 , in which the carbon atom is united with four monad 
atoms, each of the latter be placed at the extremity of one of 
the four lines which represent the valency of carbon, the 
following formulae are obtained : 

H H H 

H C H H C H Cl C Cl 

I I I 

H Cl Cl 

If in the case of substances such as C0 2 , COC1 2 , COS, each 
* Oxygen may be assumed to be a tetrad in CO. 



52 CONSTITUTION OF ORGANIC COMPOUNDS. 

of the dyad atoms be given two lines, the compounds will be 
represented by the formulae, 

o=c=o 



Similarly, HCN may be represented by the formula H C=N. 
Formulae of this kind are termed graphic formulae. They 
are intended to express in a purely diagrammatic manner the 
constitution of the several compounds that is to say, the 
state of combination and the valency of each of the atoms in 
the molecule. In all such formulae, therefore, the number of 
lines running to or from any given symbol must be the same 
as the number of monad atoms with which the element 
represented by that symbol is known to" combine. The 
constitution of carbon disulphide, for example, should not be 

expressed by the formula C^ I , or that of carbon dioxide by 

a formula such as C 0, because the valency of the 
elements is not correctly indicated by the number of lines. 

These lines are sometimes called valencies, more frequently 
bonds or linkings ; in the graphic formula H C=N", the 
hydrogen atom is said to be combined with carbon by one 
bond or linking, the nitrogen atom by three. The hydrogen 
and nitrogen atoms are not directly combined, but are both 
united with carbon. 

It must not be supposed, however, that these lines are 
intended to represent the actual force or attraction which 
causes the atoms to combine. They are simply expressions of 
valency or combining capacity, and may be shortened or 
lengthened at will without altering their significance : as a 
rule, they are shortened, as in the formulae H-CiN and 
: C : S, or brackets are employed instead, as in CH 3 (OH), 

H 

I 
which signifies the same as CH 3 -OH and H C H. All 

H 



CONSTITUTION OF ORGANIC COMPOUNDS. 53 

these, except the last, would be termed constitutional rather 
than graphic formulae, hut there is no sharp difference between 
them. 

All such formulae are based on considerations of valency, 
and on a study of the chemical behaviour of the compounds 
which they represent ; they summarise, in fact, in a concise 
and simple manner the most important chemical properties of 
those compounds. 



GHAPTEE IV. 

SATURATED HYDROCARBONS. 
THE PARAFFINS, OR HYDROCARBONS OF THE METHANE SERIES. 

It has already been noted that carbon differs from all 
other elements in forming an extraordinarily large number 
of compounds with hydrogen ; these compounds, composed 
of hydrogen and carbon only, are called hydrocarbons. 

Methane, or Marsh-gas, CH 4 , is the simplest hydrocarbon. 
It is met with, as its name implies, in marshes and other 
places in which the decomposition or decay of vegetable 
matter is taking place under water. On stirring a marshy 
pond or swamp, bubbles consisting of marsh-gas, carbon 
dioxide, and other gases frequently rise. It is one of the 
principal constituents of the gas which streams out of the 
earth in the petroleum districts of America and Eussia; it 
also occurs in coal-mines, the gas (fire-damp) which issues from 
the fissures in the coal sometimes containing as much as 
80-90 per cent, of methane, to the presence of which, mixed 
with air, explosions in coal-mines are due. Ordinary coal-gas 
usually contains about 40 per cent, of methane. 

Methane is formed* in small quantities by the direct union 

* The words formed, obtained, and produced are used when the method 
is of theoretical importance, and not suitable for the wind preparation of 
the compound. 



54 HYDROCARBONS OF THE METHANE SERIES. 

of carbon and hydrogen at about 1200; it is also obtained 
when sulphuretted hydrogen or steam, together with the 
vapour of carbon disulphide, is passed over heated copper 
(Berthelot), 

CS 2 + 2H 2 S + 8Cu = CH 4 + 4Cu 2 S 

CS 2 + 2H 2 + 6Cu = CH 4 + 2Cu 2 S + 2CuO ; 

and when carbon tetrachloride is reduced with sodium 
amalgam and water (p. 55), 



Methane is also formed when zinc methyl* (p. 222) is de- 
composed by water, 

Zn(CH 3 ) 2 + 2H 2 = 2CH 4 + Zn(OH) 2 . 

Methane is prepared by heating one part of anhydrous 
sodium or potassium acetate with four parts of soda-lime 
in a hard glass tube or retort, and collecting the gas over 
water, 

C 2 H 3 2 Na + NaOH - CH 4 + Na 2 C0 3 . 

The gas obtained in this way contains small quantities of 
hydrogen, ethylene (p. 71), and other impurities; if, how- 
ever, barium oxide be used instead of soda-lime the gas is 
evolved in a nearly pure condition. 

Pure methane is prepared by dropping a solution of methyl 
iodide in about an equal volume of 95 per cent, alcohol from 
a stoppered funnel into a flask containing a large quantity of 
a zinc-copper couple, f The methyl iodide is reduced by the 

* Compounds, such as zinc methyl, are often unavoidably introduced 
long before their properties are described; in such cases references are 
given. The groups of atoms, CH 3 -, C 2 H 5 -, C 3 H7-, and C 4 H 9 -, are termed 
methyl, ethyl, propyl, and butyl respectively (p. 117). 

f The zinc-copper couple is prepared by heating copper powder (obtained 
by reducing the oxide in hydrogen) with small pieces of clean zinc foil, or 
with zinc filings, in an atmosphere of coal-gas, until the mixture begins to 
cake together. It may also be prepared by immersing clean zinc filings in 
a 2 per cent, solution of copper sulphate, and washing first with alcohol 
and then with ether ; that prepared by the first method gives the better 
results. 



HYDROCARBONS OF THE METHANE SERIES. 55 

nascent hydrogen formed by the action of the aqueous alcohol 
on the zinc-copper couple, and a slow but continuous evolu- 
tion of methane takes place without application of heat, 



the gas is passed through a tube containing tjie zinc-copper 
couple, in order to free it from methyl iodide, and collected 
over water. 

In a similar manner, all halogen derivatives of marsh-gas 
(p. 174) are converted into marsh-gas on treatment with 
nascent hydrogen, generated in some suitable manner.* 

* The substances most frequently used in reducing organic compounds 
are, sodium and alcohol; sodium amalgam and water; zinc, iron, or tin, 
and an acid ; stannous chloride and hydrochloric acid ; hydrogen iodide ; 
sulphuretted hydrogen; and sulphur dioxide. 

Sodium, acting on an alcoholic or moist ethereal solution of the sub- 
stance, is one of the most powerful reducing agents known, 
Na + C 2 H 5 .OH = C 2 H 5 -ONa + H 

Na+H 2 0=NaOH + H. 

In cases where a high temperature is required, boiling amyl alcohol (p. 106) 
is used instead of ethyl alcohol. 

Sodium Amalgam, an alloy of sodium and mercury, acts on aqueous or 
aqueous alcoholic solutions in the same way as metallic sodium, the action 
being, however, greatly moderated by the presence of the mercury. 

Zinc and Iron are generally used with hydrochloric, dilute sulphuric, or 
acetic acid. Zinc dust is sometimes employed in alkaline solution, as, for 
instance, in the presence of potash, soda, or ammonia, 

Zn + 2KOH = Zn(OK) 2 + 2H. 

Substances which are reduced only with great difficulty are frequently 
mixed with zinc dust and heated at a high temperature. 

Tin is employed with hydrochloric acid, 

Sn + 2HCl=SnCl 2 +2H. 

Stannous Chloride is not acted on by hydrochloric acid alone, but, in 
presence of reducible substances, is a very powerful reducing agent, stannic 
chloride being formed, 

SnCl 2 + 2HC1= SnCl 4 + 2H. 

Hydrogen Iodide, in concentrated aqueous solution, is a very powerful 
reducing agent at high temperatures, being decomposed into hydrogen and 
iodine ; it is usual to add a pinch of amorphous phosphorus to the mixture, 
in order that the iodine may be reconverted into hydrogen iodide (31 +P 
+3H 2 0=H 3 P0 3 +3HI). 

Sulphuretted Hydrogen, being readily decomposed into sulphur and 



56 HYDROCARBONS OP T,HB METHANE SERIES: 

Methane is a colourless, tasteless gas; it condenses to a: 
liquid at 11 under a pressure of 180 atmospheres. It 
burns with a pale-blue, non-luminous flame-,, and forms a 
highly explosive mixture with certain proportions of air or 
oxygen, 

CH 4 + 20 2 = C0 2 + 2H 2 
2 vols. + 4 vols. = 2 vols. -t- 4 vols. 

^t is almost insoluble in water, but rather more soluble in 
alcohol. It is very stable; when passed through bromine, 
potash, nitric acid,, sulphuric acid, solution of potassium per- 
mangana^e, an,d solution of chromic acid, it is not absorbed 
or changed; in, any way. When mixed with chlorine in the 
dark, no action, takes place ; but if a mixture of 1 vol. of 
methane and. 2* vols. of chlorine be exposed to direct sunlight, 
explosion ensues, and carbon is- deposited,. 



In diffused sunlight there is no explosion, but after some" 
time a mixture of hydrogen chloride and four other com- 
pounds is produced, the proportion of each depending on. 
the quantity of chlorine present, and on the conditions of 
the experiment, 

CH 4 + C1 2 = CH 3 C1 + HCL CH 4 + 2C1 2 - CH 2 C1 2 + 2HCL 

Methyl Chloride. Methylene Chloride. 

CH 4 + 3C1 2 = CHC1 3 + 3HC1. CH 4 + 4C1 2 = CC1 4 + 4HCL 

Chloroform. Carbon Tetrachloride. 

All these compounds are formed by the displacement of one 1 
or more hydrogen atoms by an equivalent quantity of chlorine. 
The carbon atom cannot combine with more than four monad ; 
atoms, so that hydrogen must be displaced if any action at all 
take place. Now, it may be supposed that in the formation 
of methyl chloride, CH 3 C1, for example, one of the hydrogen 

hydrogen, is frequently used as a mild reducing agent, generally in the 
form of ammonium sulphide. 

Sulphur Dioxide has only a limited use ; in presence of water and re-- 
ducible substances, it is converted into sulphuric acid, 
SO 2 + 2H 2 O = H 2 SO 4 + 2H. 




HYDROCARBONS OF THE METHANE SERIES. 57 

atoms is drawn away from the carbon by the superior attrac- 
tion of the chlorine, and that one atom of chlorine takes up 
the vacant place in the molecule without the other atoms 
being disturbed or their state of combination altered; this 
change may then be represented graphically thus : 

1 H 

+ I 
Cl 

In the formation of methylene chloride, CH 2 C1 2 , it may be 
supposed that a repetition of this process occurs, and so also 
in the case of the other products ; in other words, it may be 
assumed that in all the above examples the action of 
the chlorine is not such that the molecule of marsh-gas is 
completely broken up into atoms, which then, by combination 
with chlorine, form totally new molecules, but that certain 
atoms simply change places. To such changes as these, in 
which certain atoms are simply displaced by an equivalent 
quantity of other atoms, without the state of combination of 
the rest of the molecule being altered, the term substitution 
is applied, and the compounds formed as the result of the 
^change are called substitution products. 

The four compounds mentioned above are substitution 
products of methane and of one another : methyl chloride, 
'CH 3 C1, is a mono-substitution product, methylene chloride, 
'CH 2 C1 2 , a di-substitution product of marsh-gas, and so on; 
chloroform, CHC1 3 , is a tri-substitution product of methane, 
a di-substitution product of methyl chloride. If, by treat- 
ment with nascent hydrogen in the manner described above, 
any of these substitution products be reconverted into marsh- 
gas or into one another, the change would be termed inverse 
substitution. 

The only way in which it is possible to produce a change 
in marsh -gas, or in any of its chloro-substitution products, 
is by a process of direct or inverse substitution. The atom of 
carbon already holds in combination its maximum number 



58 HYDROCARBONS OF THE METHANE SERIES. 

of atoms, and some of them must be displaced if any other 
atom enter the molecule. Compounds such as these, in 
which the maximum combining capacity of all the carbon 
atoms is exerted, and which can only yield derivatives by 
substitution, are termed saturated. 

Ethane, ethyl hydride, or dimethyl, C 2 H 6 , like methane, 
occurs in the gas which issues from the earth in the 
petroleum districts. It is formed when methyl chloride 
or methyl iodide is treated with sodium in dry ethereal 
solution, 

2CH 3 I + 2Na = C 2 H 6 + 2NaI ; 

this reaction affords a means of preparing ethane from its 
elements, because methane can be formed by the direct 
union of its elements, as already stated, and then converted 
into methyl chloride by treatment with chlorine. 

Ethane is also formed when zinc ethyl (p. 220) is decom- 
posed with water, 

Zn(C 2 H 6 ) 2 + 2H 2 - 2C 2 H 6 + Zn(OH) 2 ; 
when ethylene (p. 71) is treated with nascent hydrogen, 

C 2 H 4 + 2H = C 2 H 6 ; 
and when methyl iodide is treated with zinc methyl, 



Ethane is prepared by reducing ethyl iodide with the zinc- 
copper couple, exactly as described in the preparation of pure 
methane, 



or by the electrolysis of dilute acetic acid, or of a concen- 
trated aqueous solution of potassium acetate -(Kolbe). When 
acetic acid is used, ethane and carbon dioxide are evolved at 
the positive, hydrogen at the negative, pole, 

CH 3 -C0 2 H 

= 



when potassium acetate is employed the following decom- 
positions occur : 



HYDROCARBONS OF THE METHANE SERIES. 59 



and 



so that the same gases are evolved as before. 

Ethane is a colourless, tasteless gas, which liquefies at 
4 under a pressure of 46 atmospheres; it is practically 
insoluble in water, slightly soluble in alcohol. It is in- 
flammable, burns with a feebly luminous flame, and can be 
exploded with air or oxygen, 

2C 2 H 6 + 70 2 - 4C0 2 + 6H 2 
4 vols. + 14 vols. = 8 vols. + 12 vols. 

It is very stable, and is not acted on by alkalies, nitric acid, 
sulphuric acid, bromine, or oxidising agents at ordinary 
temperatures. When mixed with chlorine and exposed to 
diffused sunlight, it gives various substitution products, 1, 2, 
3, 4, 5, or 6 atoms of hydrogen being displaced by an 
equivalent quantity of chlorine, 

C 2 H 6 + C1 2 = C 2 H 5 C1 + HC1. C 2 H 6 + 2C1 2 = C 2 H 4 C1 2 + 2HC1. 

Ethyl Chloride. Ethylene Bichloride. 



Perchlorethane. 

Ethane, like methane, cannot combine directly with chlorine 
or with any element j it is a saturated compound. 

The constitution of ethane may be deduced theoretically in 
the following manner : the two atoms of carbon must be 
directly united, because hydrogen, being monovalent, cannot 
link the two carbon atoms together ; as, moreover, carbon is 
tetravalent, each of the carbon atoms must also be directly 
united with three atoms of hydrogen as represented in 

H H 

the following graphic formula, H C C H. This view, 

H H 

based entirely on considerations of valency, is confirmed 



60 HYDROCARBONS OF THE METHANE SERIES. 

by a study of the methods of formation and properties of 
ethane. When methyl iodide is treated with sodium or 
with zinc methyl, the metal combines with the halogen, 
and a group of atoms, CH 3 -, is left; as, however, carbon is 

H 

tetravalent, this group H C , like the atom of hydrogen 

H 

H-, cannot exist alone, and immediately combines with a 
similar group forming ethane, CH 3 -CH 3 , or dimethyl, which 
is a saturated compound, because all the carbon atoms in the 
molecule are exerting their maximum valency or combining 
capacity. 

Propane, propyl hydride, or methyl-ethyl, C 3 H 8 , occurs in 
petroleum, and can be obtained by reducing propyl iodide or 
isopropyl iodide (p. 181) with zinc and hydrochloric acid, or 
with the zinc-copper couple, 



It i also obtained by heating a mixture of ethyl and methyl 
iodides with sodium in ethereal solution, 

C 2 H 5 T + CH 3 I + 2Na = C 3 H 8 + 2NaI, 

and by treating zinc ethyl with methyl iodide, 

Zn(C 2 H 5 ) 2 + 2CH 3 I = 2C 3 H 8 + ZnI 2 . 

Propane is a gas, and closely resembles methane and ethane 
in chemical properties. It condenses to a colourless liquid at 
temperatures below 17 under ordinary atmospheric pressure. 
It burns with a more luminous flame than ethane. When 
treated with chlorine in diffused sunlight, it yields propyl 
chloride and other substitution products, one or more hydro- 
gen atoms being displaced, 



Constitution. Since propane is produced by the action of 
sodium on a mixture of methyl and ethyl iodides, and also 



HYDROCARBONS OF THE METHANE SERIES. 61 

by the action of zinc ethyl on methyl iodide, it is concluded 

H 

that propane is formed by the combination of C H and 

H H H 

H C C ; its constitution is therefore represented by the 

U 

H H H 
formula H-C C C H, or CH 3 .CH 2 .CH 3 , and it may be 

H H H 

regarded as derived from ethane, just as ethane may 
be considered as derived from methane, by substituting 
the monovalent group of atoms CH 3 - for one atom of 
hydrogen. 

Butanes, C 4 H 10 . Two hydrocarbons of the molecular 
formula C 4 H 10 are known. One of them, butane, diethyl or 
methyl-propyl, occurs in petroleum, and can be obtained by 
heating ethyl iodide with sodium in ethereal solution, 

2C 2 H 5 I + 2Na = C 4 H 10 + 2NaI. 

The other, isobutane, or trimethylmethane, is formed when 
tertiary butyl iodide (p. 181) is reduced with nascent 
hydrogen, 



These two hydrocarbons have been proved to have the same 
molecular formula, but to be different in properties. Although 
they are both gases under ordinary conditions, butane liquefies 
at about 0, isobutane not until about 17 under atmospheric 
pressure, so that they are certainly distinct substances. In 
chemical properties they closely resemble propane and one 
another. They give substitution products with chlorine, but 
the compounds obtained from butane are not identical with 
those produced from isobutane, although they have the same 
molecular formulae. 

Constitution of the two Butanes. The production of butane 



62 HYDROCARBONS OF THE METHANE SERIES. 

from ethyl iodide in the above-mentioned manner indicates 
that this hydrocarbon is di-ethyl. It is therefore represented 
by the formula, 
H H H H 

H-C-C-C-C-H, or C 2 H 5 -C 2 H 5 , or CH 3 .CH 2 .CH 2 .CH 3 , 

' 



which not only brings to mind the method of formation of 
the hydrocarbon, but also indicates its relation to propane. 
Butane, in fact, may be regarded as propane in which one 
atom of hydrogen has been displaced by the monovalent 
CH 3 - group. When, however, the graphic formula of pro- 
pane is carefully considered, it will be seen that the eight 
atoms of hydrogen are not all in the same state of com- 
bination relatively to the rest of the molecule, but that two 
of them (a), 

(a) 
H H H 

H-i-C-i-H, or CH 3 -CH 2 -CH 9 , or CH 2 (CH 3 ) 2 
i A i (a) (a) 

(a) 

are united with a carbon atom which is itself combined with 
two carbon atoms, whereas each of the other six atoms of 
hydrogen is combined with a carbon atom which is united 
with only one other. If, then, one of the (a) hydrogen atoms 
be displaced by a CH 3 - group, the constitution of the product 
would be represented by the formula, 
H H H 

H-C - C - C-H, or CH 3 -CH-CH 3 , or CH(CH 3 ) 3 
H H CH 8 

Isobntane. 
(n.) 

whereas, if one of the other hydrogen atoms were displaced, a 




HYDROCARBONS OP THE METHANE SERIES. 63 

hydrocarbon of the constitution represented by formula i. 
would be formed. As in these two cases the atoms would 
not all be in the same state of combination, the properties 
of the compounds represented by these formulae would be 
different. 

It is next important to note that the above two are the only 
formulae which can be constructed with four atoms of carbon 
and ten atoms of hydrogen, if it be assumed that carbon is 
tetravalent and hydrogen monovalent. All formulae such as 

H 

TT 1 

-y 

H H 

TT/ - or 




H/ 

/ 

H/ 

will, on examination, be found to be identical with i. or IL, 
as they express the same state of combination. Since, then, 
formula i. represents the constitution of butane, that of iso- 
butane or trimethylmethane is expressed by formula u. This 
conclusion is confirmed by a study of the methods of forma- 
tion and chemical behaviour of isobutane. 

Pentanes. Three hydrocarbons of the molecular formula 
C 5 H 12 are known ; two of them namely pentane (b.p. 37) * 
and isopentane (b.p. 30) occur in petroleum, and are colour- 
less mobile liquids. The third, tetramethylmethane (b.p. 
9-5), can be obtained by treatfng tertiary butyl iodide (p. 181) 
with zinc methyl, 

2(CH 3 ) 3 CI + Zn(CH 3 ) 2 = 2(CH 3 ) 3 C-CH 3 + ZnI 2 . 

For reasons similar to those stated in the case of the simpler 
hydrocarbons, the constitutions of the three pentanes are 
respectively represented by the formulae, 

* Except when otherwise stated, all the boiling-points given in this book 
refer to ordinary atmospheric pressure. 




64 HYDROCARBONS OF THE METHANE SERIES. 



HHHHH HHH 

H 6 C C C C H H C C C 

HHHHH H H 

I x -n 

H-C-H 

A 

Pentane. Isopentane. Tetraniethylmethane.. 

They may all be regarded as derived from the butanes (pen- 
tane and isopentane from normal butane,* tetramethylmethane 
from isobutane) by the substitution of a CH 3 - group for one 
atom of hydrogen. 

Isomerism. Compounds, such as the two hydrocarbons; 
C 4 H 10 , and the three hydrocarbons C 5 H 12 , which have re- 
spectively the same molecular formula, but different constitu- 
tions, are said to be isomeric. The phenomenon is spoken 
of as isomerism, and the compounds themselves are called 
isomers or isomerides. Isomerism is due to a difference 
in the state of combination or arrangement of the atoms. 

When graphic formulae are employed to represent the con- 
stitutions of the hydrocarbons, it will be found possible to 
construct as many different formulas as there are isomerides. 
It is possible, for example, to construct three different graphic 
formulae for a substance of the molecular formula C 5 H 12 , and 
three isomerides only are known; more could not be repre- 
sented by graphic formulae, assuming always that carbon is 
tetravalent. This agreement between theoretical conclusions 
and observed facts is strong evidence of the tetravalent 
character of carbon. 

Ethane may be regarded as derived from methane, propane 
from ethane, and the butanes from propane, by substitut- 
ing the monovalent group of atoms CH 3 - for one atom of 
hydrogen, and, theoretically, this process can be continued 
without limit. If one hydrogen atom in each of the three 
* Compare p. 65. 



TTYmiOCARBONS OF THE METHANE SERIES. 65 

jpentanes be displaced : by a CH 3 - group, a number of iso- 
iiiieric hydrocarbons, 'C 6 H 14 , would be obtained, from each of 
which, by a repetition of the same process, at least one hydro- 
carbon, C-H 16 , might be formed, and so on. It is evident, 
then, that, theoretically, a great number 'of hydrocarbons may 
( exist ? and, as a matteT of fact, very many have actually been 
isolated from petroleum (p. '69). As the number of carbon 
atoms in the molecule increases, the number of possible 
isomerides rapidly becomes larger ; 7 isomerides of the 
molecular formuk C ? H 16> 18 of the formula C 8 H 18 , and no 
less than 02 of the formula C 13 H 28 could, theoretically, be 
formed. In many cases, all the possible isomerides have not 
been prepared, but there can be little doubt that they could 
be obtained by suitable reactions. 

The several isomerides are usually distinguished by the terms 
normal or primary, iso- or secondary, and tertiary. A normal or 
primary hydrocarbon is one in which no carbon atom is directly 
combined with more than two others, as, for example, 

CH 3 -CH 2 .CH 2 .CH 3 CHs-CH^CHyCHo-CH^CHs. 

Normal Butane. Normal Hexane. 

A secondary or iso-hydrocarbon contains at least one carbon atom 
directly united with three others, 



CH 3 CH 3 

Isobutane (or Trimethylmethane). Di-isopropyl. 

A tertiary hydrocarbon contains at least one carbon atom directly 
combined with four others, 

CH 3 CH 3 

CH 3 - C - CH 3 CH 3 - C - CH 2 - CH 3 

CH 3 CH 3 

Tertiary Pentane Tertiary Hexane 

(or Tetranietliylinetliane). (or Triinethylethylniethane). 

In the case of iso- and tertiary hydrocarbons, it is convenient to use 
a name which readily expresses the constitution of the compound ; 
examples of such names are given above in brackets. 

Drg. B 



66 HYDROCARBONS OF THE METHANE SERIES. 

The hydrocarbons methane, ethane, propane, &c. are not 
only all produced by similar reactions, but they also show 
very great similarity in chemical properties ; for these reasons 
they are classed together as the paraffins, or hydrocarbons of 
the methane series. The class, or generic, name ' paraffin ' was 
assigned to this group because paraffin-wax consists principally 
of the higher members of the methane series. Paraffin-wax is 
a remarkably inert and stable substance, and is not acted on by 
strong acids, alkalies, &c. ; the name paraffin, from the Latin 
parum affinis (small or slight affinity), was given to it for this 
reason. 

Homologous Series. When the paraffins are arranged in 
order of increasing molecular weight they form a series, each 
member of which contains one atom of carbon and two atoms 
of hydrogen more than the preceding member. 

Methane, CH^ j 
Ethane, C 2 H 6 { 
Propane, C 3 H 8 { 
Butane, C 4 H 10 
Pentane, C 5 H 12 f 

The members of this series are similar in constitution 
and in chemical properties; but as the molecular weight 
increases, the physical properties undergo a gradual and 
regular variation. Such a series is termed homologous, 
and the several members are spoken of as homologues of 
one another; there are many homologous series of organic 
compounds. 

General Formulae. The molecular composition of all the 
members of a homologous series can be expressed by a general 
formula. In the case of the paraffin series the general formula 
is C w H 2M+2 ) which means, that in any member containing n 
atoms of carbon in the molecule, there are 2n + 2 atoms of 
hydrogen ; in propane, C 3 H 8 , for example, n = 3 ; 2w + 2 = 8. 
That this is so can be readily seen by writing the graphic 
formulae of some of the paraffins in the following manner : 



HYDROCARBONS OF THE METHANE SERIES. 67 

H HH HHH 

H C H H C-C H H C-C-C H 

H HH HHH 

when it is at once obvious that for every atom of carbon there 
are two atoms of hydrogen, the molecule containing, in addi- 
tion, two extra hydrogen atoms. 

Since the members of a homologous series can, as a rule, 
be obtained by similar or general methods, if these be given 
it is usually unnecessary to describe the preparation of each 
member separately. In view, also, of the great similarity in 
chemical properties, a detailed account of each compound 
may be omitted if the general properties of the members 
of the series be described ; the physical properties may 
also be treated in a general manner, since they undergo 
a regular and gradual variation as the molecular weight 
increases. 

The following is a summary of the principal facts relating 
to the paraffins treated in this way ; it will be found advan- 
tageous to omit this and other summaries until some knowledge 
of other series has been acquired. 

SUMMARY AND EXTENSION. 

The Paraffin or Methane Series. Saturated hydrocarbons of 
the general formula C M H 2M +2. The more important members of 
the series are the following, the number of possible isomers being 
indicated by the figures in brackets : 

Methane (1), CH 4 Hexane (5), C 6 H 14 

Ethane (1), C 2 H 6 Heptane (9), C 7 H 16 

Propane (1), C 3 H 8 Octane (18), C 8 H 18 

Butane (2), C 4 H 10 Nonane (35), CgH^ 

Pentane (3), C 5 H 12 Decane (75), C 10 H 22 

Nomenclature. The names of all the hydrocarbons of this series 
have the distinctive termination ane, those of the higher members 
having a prefix which denotes the number of carbon atoms in the 
molecule. 

Occurrence. The paraffins are found in nature in enormous 
quantities as petroleum or mineral naphtha, in smaller quantities 
as natural gas, and as earth -wax, or ozokerite. 



68 HYDROCARBONS OF THE METHANE SERIES. 

Methods of Preparation. (1) By the dry distillation of an alkali 
salt of a fatty acid (p. 145) with potash, soda, or soda-lime, 

CH 3 .COONa + NaOH = CH 4 + Na 2 CO 3 
C 3 H 7 .COOK + KOH = C 3 H 8 + K 2 CO 3 . 

(2) By the action of nascent hydrogen on the alkyl* halogen 
compounds, 

CHC1 + 2H = C 



(3) By the action of sodium or zinc on the alkyl halogen com- 
pounds (Wtirtz), 

2C 2 H 5 I + 2Na = C 2 H 5 -C 2 H 5 + 2NaI 
2CH 3 I + 2Na = CH 3 .CH 3 + 2NaI. 

(4) By decomposing the zinc alkyl compounds (p. 220) with water 
(Frankland), 

Zn(CH 3 ) 2 + 2H 2 O = 2CH 4 + Zn(OH), 
Zn(C 3 H 7 ) 2 + 2H 2 O = 2C 3 H 8 + Zn(OH) 2 . 

(5) By the action of the alkyl halogen compounds on the zinc 
alkyl derivatives, 

2CH 3 I + Zn(CH 3 ) 2 =2CH 3 .CH 3 + ZnI 2 
2CH 3 I + Zn(C 2 H 5 ) 2 = 2CH 3 -C 2 H 5 + ZnI 2 . 

Tertiary hydrocarbons, such as tetramethyl methane, may be 
similarly prepared by acting with the zinc alkyl compounds on 
certain dihalogen derivatives of the paraffins (p. 142), 



(6) By the electrolysis of aqueous solutions of the sodium or 
potassium salts of the fatty acids (Kolbe), 

2CH 3 -COOK + 2H 2 O = CH 3 -CH 3 + 2C0 2 + 2KOH + H 2 . 

Physical Properties. The first four members of the series are 
colourless gases under ordinary conditions, but they are liquefied 
fairly easily and the more readily the greater the number of carbon 
atoms in the molecule. Methane liquefies at - 11 under a pressure of 
180 atmospheres, ethane at 4 under 46 atmospheres, butane at 
under ordinary atmospheric pressure. The hydrocarbons contain- 
ing from 5 to about 16 atoms of carbon are colourless liquids 
under ordinary conditions, the boiling-point rising as the series is 
ascended. Normal pentane boils at 37, normal hexane at 69, and 
normal heptane at 98, the difference between the boiling-points 
of consecutive normal hydrocarbons being about 30. The higher 

* The meaning of the word alkyl is given on p. 117. 



HYDROCARBONS OF THE METHANE SERIES. 69 

members of the series, from about C 16 H 34 (m.p. 18), are colourless 
solids, the melting-point rising with increasing molecular weight. 

The specific gravity of the hydrocarbons from butane, C 4 H 10 , to 
octane, C 8 H 18 , varies from 0-600 to about 0-718 ; from octane 
upwards the sp. gr. increases until the solid hydrocarbons are 
reached, when it becomes almost constant at 0-775-0-780, this 
value being determined at the melting-point. 

The paraffins are insoluble, or nearly so, in water, but soluble in 
alcohol, ether, and other organic liquids. 

Chemical Properties. The paraffins are all characterised by 
great stability. At ordinary temperatures they are not acted on by 
nitric acid, fuming sulphuric acid, alkalies, or such powerful oxidis- 
ing agents as chromic acid and potassium permanganate, and even 
at higher temperatures only a very slow action occurs. They are, 
however, attacked by chlorine and, less readily, by bromine in 
sunlight with formation of substitution products. Iodine has no 
action on the paraffins. 

The paraffins are saturated compounds, and cannot combine 
directly with any element. 

Paraffins of Commercial Importance. In Pennsylvania, North 
America ; in Baku, South-east Russia ; and in other parts of the 
world, a gas escapes from the earth under considerable pressure, 
either spontaneously or as the result of boring. This natural gas 
is variable in composition, but usually contains a large propor- 
tion of methane and hydrogen, small quantities of other gaseous 
paraffins, and other hydrocarbons. It is employed as a fuel at 
Pittsburgh in Pennsylvania for a variety of industrial purposes. 

In the localities already mentioned enormous quantities of 
petroleum or mineral naphtha are also obtained, either from 
natural springs or from artificial borings. The origin of natural 
gas and petroleum is unknown, but it is possible that they are 
produced by the destructive distillation in the lower layers of the 
earth's crust of the fatty remains of (sea) animals, or by the action 
of water on carbides. 

Crude petroleum is specifically lighter than water, and varies 
greatly in consistency and colour, being generally a thick yellow or 
brown liquid with a greenish colour when viewed by reflected light. 
t consists almost entirely of a mixture of hydrocarbons, that 
obtained from Pennsylvania being composed chiefly of paraffins, 
that from Baku of hydrocarbons belonging to a different (naphthene) 
series. 

Petroleum is not only, next to coal-gas, one of the most important 
illuminating agents of the present day, but is also the source of a 



70 HYDROCARBONS OF THE METHANE SERIES. 

number of substances of considerable commercial value. The crude 
oil is not directly employed for illuminating purposes, owing partly 
to the fact that it contains very volatile hydrocarbons which render 
it too inflammable. In order to obtain the various substances in 
a condition suitable to the purposes for which they are required, 
the crude oil is distilled from large iron vessels and the distillate 
collected in fractions. American petroleum, treated in this way, 
yields: Petroleum ether (b.p. 40-70), gasoline (b.p. 70-90), and 
ligroin or light petroleum (b.p. 80-120), colourless mobile liquids 
used as solvents for resins, oils, caoutchouc, &c. ; cleaning oil (b.p. 
120-170), employed for cleaning purposes, and as a substitute for 
oil of turpentine in the preparation of varnishes ; refined petroleum, 
kerosene, or burning oil (b.p. 150-300), used for illuminating pur- 
poses ;* the portions collected above 300 are employed as lubri- 
cating oils, vaseline, &c., and the residual carbonaceous mass is 
used for electrical purposes. Russian petroleum also yields a 
variety of products, such as benzine, kerosene, Vulcan oil, vaseline, 
and paraffin, which, though slightly different in composition, are 
similar in properties and uses to those obtained from American oil. 

Ordinary paraffin-wax is also obtained from the tar which 
is produced by the destructive distillation of cannel-coal or shale. 
When this tar is fractionally distilled, it yields several liquid pro- 
ducts similar to those obtained from petroleum such as photogene 
and solar oil, which are used as solvents and for illuminating 
purposes and solid paraffins, or paraffin-wax, which is purified by 
treatment with concentrated sulphuric acid and redistillation. 
Paraffin-wax is a colourless, semi-crystalline, waxy substance, 
soluble in ether, &c., but insoluble in water; its melting-point 
ranges from about 45-65, according to its composition ; its prin- 
cipal use is for the preparation of candles (p. 173). 

Ozokerite is a naturally occurring solid paraffin or earth-wax 
which is found in Galicia and Roumania ; it is purified by treat- 
ment with concentrated sulphuric acid and distillation. 

* All petroleum products of low boiling-point are highly infiai 
and form explosive mixtures with air (use in gas-engines) ; they should 
be handled with extreme caution. 



HYDROCARBONS OF THE ETHYLENE SERIES. 71 



CHAPTER V. 

UNSATUBATED HYDROCARBONS. 
THE OLEFINES, OR HYDROCARBONS OF THE ETHYLENE SERIES. 

When the halogen mono-substitution products of the 
paraffins, such as ethyl bromide, propyl chloride, &c. (p. 174), 
are heated with an alcoholic solution of potash, they are con- 
verted into hydrocarbons, 

C 2 H 5 Br + KOH = C,H 4 + KBr + H 2 
C 3 H 7 C1 + KOH = CgH 6 + KC1 + H 2 O. 

The compounds obtained in this way, and by other methods 
to be described later, contain two atoms of hydrogen less 
than the corresponding paraffins, and form a homologous 
series of the general formula C n H^ n ; their names are derived 
from those of the corresponding paraffins by changing the 
termination ane into ylene, 

Methane, CH 4 ; Ethane, C 2 H 6 ; Propane, C 3 H g ; Butane, CjH^ 
Ethylene, C 2 H 4 ; Propylene, C 3 H 6 ; Butylene, C 4 Hg. 

The simplest member of the series is ethylene; the hydro- 
carbon CH 2 (methylene), which would correspond with 
methane, is unknown, and all attempts to prepare it have 
been unsuccessful ; this seems to show that a compound in 
which carbon would be divalent is incapable of existing. 

The word 'olefine' is derived from 'olefiant' or 'oil- 
making ' gas, a name originally given to ethylene on account 
of its property of forming an oily liquid (ethylene dichloride 
or Dutch liquid) with chlorine ; the term ' olefine ' is now 
applied as a generic or class name to all the hydrocarbons of 
the series. 

Ethylene, ethene, or defiant gas, C. 7 H 4 , is formed during the 
destructive distillation of many organic substances, and occurs 
in coal gas, of which it forms about 6 per cent by volume ; 



72 HYDROCARBONS OP THE ETHYLBNE SERIES. 

the luminosity of the burning gas is to a great extent due to 
ethylene. 

It is formed when acetylene (p. 81) in the form of copper 
acetylide is reduced with zinc dust and ammonia, 



and when methylene iodide is heated with copper at 100 in 
a sealed tube, 

2CH 2 I 2 + 4Cu - a,H 4 + 2Cu 2 I 2 , 

a reaction which is very similar to the formation of ethane by 
the action of sodium on, methyl iodide (p. 58). 

Ethylene is also obtained when a solution of potassium 
succinate (p. 240) is submitted to electrolysis (Kekule), 

C 2 H 4 (COOK) 2 = C 2 H 4 + 2C0 2 + 2K, 

a mixture of ethylene and carbon dioxide being obtained 
at the positive pole, the alkali metal which separates at the 
negative pole acting on the water with liberation of hydrogen. 
This interesting method of formation of ethylene recalls the 
production of ethane by the electrolysis of potassium acetate 
(p. 68). 

Ethylene is prepared by heating ethyl alcohol with concen- 
trated sulphuric acid or with phosphoric acid ; the reaction 
may be expressed by the equation, 



but in reality it is not so simple (p. 186). 

A mixture of ethyl alcohol (25 g.) and concentrated sulphuric acid 
(150 g.) is placed in a capacious flask (fig. 17) and heated to about 
165, the gas thus produced being passed first through water and 
then through a solution of potash, to free it from sulphur dioxide 
and carbon dioxide, and finally collected over water; when the 
evolution of gas slackens, a further supply may be obtained by 
dropping a mixture of 1 part of alcohol and 2 parts by weight 
of sulphuric acid through the funnel, the temperature being kept 
constant. The liquid in the flask generally darkens considerably, 
owing to the oxidising action of the acid, and unless good alcohol 
be used a large quantity of carbonaceous matter is often formed. 
For this reason phosphoric acid may be advantageously employed, 



HYDROCARBONS OF THE ETHYLENB SERIES. 73 

in which case the alcohol is dropped into syrupy phosphoric acid 
heated at about 220 ; the yield by this method is good, and the 
gas does not require purifying. 

Another method for the preparation of etliylene is to drop 
ethyl bromide from a stoppered funnel into a flask containing 
boiling alcoholic potash, 

C 2 H 5 Br + KOH = C 2 H 4 + KBr + H 2 0. 

The flask is heated on a water-bath, and provided with a reflux 
condenser (p. 190), the end of which is connected to a delivery tube 
passing- to the pneumatic trough. 




Fig. 17. 

Ethylene is a colourless gas, has a peculiar sweet but not 
unpleasant smell, and liquefies at 10 under a pressure of 
60 atmospheres ; it is only sparingly soluble in water, more 
readily in alcohol and ether. It burns with a luminous 
flame, and forms a highly explosive mixture with air or 
oxygen, 

C 2 H 4 + 30 2 = 2C0 2 + 2H 2 
2 vols. + 6 vols. = 4 vols. + 4 vols. 



74 HYDROCARBONS OF THE ETHYLENE SERIES. 

Its chemical behaviour is totally different from that of the 
paraffins. It combines directly with hydrogen at high 
temperatures (in presence of spongy platinum at ordinary 
temperatures) forming ethane, 

C 2 H 4 + H 2 = C 2 H 6 . 

Although it is not acted on by hydrochloric acid, it com- 
bines directly with concentrated hydrobromic and hydriodic 
acids at 100, forming ethyl bromide and ethyl iodide 
respectively, 

C 2 H 4 + HBr = C 2 H 5 Br C 2 H 4 + HI = C 2 H 5 L 

It combines directly with chlorine and bromine, and also 
with iodine in alcoholic solution, 

C 2 H 4 + X 2 = C 2 H 4 X 2 (X = Cl,Br,I). 

It is absorbed by, and combines directly with, fuming 
sulphuric acid, and, more slowly, with ordinary sulphuric 
acid, yielding ethyl hydrogen sulphate (p. \85), 

C 2 H 4 + H 2 so 4 = C.HS-HSO,. 

Constitution of Ethylene. Ethylene is formed when ethyl 
bromide, a mono-substitution product of ethane, is heated with 
alcoholic potash, which simply takes away one atom of hydrogen 
and one atom of bromine (C 2 H 5 Br = C 2 H 4 + HBr) ; since, there- 
fore, the constitution of ethyl bromide is represented by the 
formula, 

H H H H 

\ I () II 

H C C H, that of ethylene would be H-C-C (i.), 
(&) I I I 

H Br H 

assuming that one of the (a) hydrogen atoms were taken away, 
H H 

H C C H (H.) if one of the (b) hydrogen atoms were 
removed. 

But if ethylene have the constitution (i.), ethylene di- 
bromide, C 2 H 4 Br 2 (p. 77), the compound formed by the direct 
combination of ethylene with bromine, must be represented by 



HYDROCARBONS OF THE ETHYLENE SERIES. 75 

H H 

the formula (in.), H C C Br, because, from the behaviour 

H Br 

of the paraffins, it is known that the carbon atom in the CH 3 - 
group cannot combine with bromine except by substitution. 
As, however, a substance C 2 H 4 Br 2 (ethylidene dibromide, 
p. 142), whose constitution must be represented by the formula 
(in.), is known, and is not identical with ethylene dibromide, 
the latter cannot have the same constitution, but must be 

H H 

represented by the only alternative formula, H C C H. 

Br Br 

This being the case, the constitution of ethylene might 
be expressed by formula (H.). But such a formula does 
not indicate that carbon is tetravalent, nor does it recall the 
fact that ethylene combines directly with C1 2 , Br 2 , HBr, &c. 
These deficiencies might be remedied by writing ethylene 
H H 

H C C H to show that the carbon atoms are tetravalent 

I I 

but that their combining capacity is not fully exercised ; this 
formula would indicate the fact that each of the carbon atoms 
has still the power of combining with one monad atom or 
group. It is usual, however, to represent the constitution of 
H H 

ethylene by the formula H-C=C-H or CH 2 = CH 2 orCH 2 :CH 2 , 
the two carbon atoms being joined by two lines, bonds, or 
linkings ; this formula is not quite the same as that just given, 
because it indicates that the particular portion of the com- 
bining power of each of the carbon atoms, which before was 
represented as doing nothing, or free, is in some way exerted 
in ' satisfying,' or combining with, the other carbon atom. 
There are at least two very good reasons for writing the 



76 



HYDROCARBONS OF THE ETHYLENE SERIES. 



formula in this way and not with unoccupied lines, or free 
bonds; firstly, because it has been found impossible to 

H H 

prepare hydrocarbons such as H C , C , or C H, a fact 

H H 

which indicates that no carbon compound can exist in which 
the maximum combining capacity of the carbon atom or 
atoms is not exerted in some way ; secondly, because when- 
ever a compound contains one carbon atom which is not 
combined with the maximum quantity of four monad atoms 
or their valency equivalent, the carbon atom directly united 
with it is in the same 'unsatisfied' condition. One has 
never been found to exist without the other, and so it is 
assumed that they have some action on one another. 

The above view of the constitution of ethylene receives support 
from the formation of the gas by the electrolysis of succinic acid, 
as is clearly seen if the decomposition be represented thus : 

CH 2 -COOH CH 2 - C0 2 H- CH 2 H 

| =| + + =|| +2C0 2 + | ; 

CH 2 .COOH CH 2 - CO 2 H- CH 2 H 

again, the formation of ethylene by the action of copper on 
methylene iodide can only be explained on the assumption that 
ethylene has this constitution, 

CH 2 

: || + 2CU 2 I 2 . 

CH 2 

All organic compounds, which, like ethylene, contain 
carbon atoms having the power of combining directly with 
other atoms or groups, are said to be unsaturated. In 
the graphic formulas of all such substances, these particular 
carbon atoms are represented as joined by a double bond or 
double linking. "When an unsaturated compound enters 
into direct combination, the double bond is said to be broken, 
and the two carbon atoms, which before were written with 
two lines between them, are now joined by only one; the 




HYDROCARBONS OP THE ETHYLENE SERIES. 77 

combination of ethylene with bromine, for example, is 
expressed graphically, 

H H H H 

C = C + Br Br = Br C C Br, 



and its formula shows that ethylene dibroniide, like the 
paraffins, is a saturated substance, and cannot combine 
except by substitution. 

The substances formed by the direct union of unsaturated 
compounds with atoms or groups of atoms are called additive 
products, in contradistinction to substitution products. Un- 
saturated compounds always combine with 2, 4, 6, &c., 
monovalent atoms or groups, because they always contain 
an even number of unsaturated carbon atoms. 

Derivatives of Ethylene. Ethylene dichloride, C 2 H 4 C1 2 , or 
CH 2 C1-CH 2 C1, was originally called Dutch liquid, or oil of 
Dutch chemists, by whom it was discovered. It is obtained 
by the direct combination of ethylene and chlorine, and is 
a colourless liquid of sp. gr. 1-28 at 0, boiling at 85. 
It is isomeric with ethylidene chloride, CH 3 -CHC1 2 (p. 142). 
Ethylene dibromide, C 2 H 4 Br 2 , orCH 2 Br-CH 2 Br, is prepared by 
passing ethylene into bromine until the colour of the latter 
disappears; the product is purified by distillation. It is a 
colourless crystalline substance, melts at 9-5, and boils at 
131; its sp. gr. is 2-21 at 0. It is isomeric with ethylidene 
bromide, CH 3 .CHBr 2 (p. 142). 

Substitution products of ethylene, such as chlorethylene or 
vinyl chloride, CH 2 :CHC1, bromethylene or vinyl bromide, 
CH 2 :CHBr, cannot be obtained by treating ethylene with 
a halogen, because additive products are produced in this 
way. They are the first products of the action of alcoholic 
potash on the halogen additive products of ethylene (p. 82), 

CH 2 Br-CH 2 Br + KOH = CH 2 :CHBr + KBr + H 2 0. 

Vinyl chloride is a gas, vinyl bromide a colourless liquid, 



78 HYDROCARBONS OF THE ETHYLENE SERIES. 

boiling at 16; they are unsaturated compounds, and combine 
directly with Br 2 , HBr, &c. 

Propylene or methyl-ethylene, C 3 H 6 , or CH 3 -CH:CH 2 , is 
formed by the dehydrating action of phosphorus pentoxide on 
propyl alcohol (p. 105), 

CH 3 -CH 2 .CH 2 .OH = CH 3 .CH:CH 2 + H 2 0. 

It is prepared by boiling either propyl or isopropyl bromide 
with alcoholic potash, 

Propyl bromide, CH 3 -CH 2 .CH 2 Br 
Isopropyl bromide, CH 3 .CHBr.CH 3 = 

It is a gas very similar to ethylene in properties ; it liquefies 
at ordinary temperatures under a pressure of 7-8 atmospheres, 
and being an unsaturated compound, combines readily with 
bromine, forming propylene dibromide, CH 3 -CHBr-CH 2 Br, 
an oily liquid boiling at 141. 

The higher members of the olefine series are obtained by 
methods similar to those employed in the case of propylene. 
Three isomeric butylenes of the molecular formula C 4 H 8 are 
known, namely, 



CH 3 .CH 2 .CH:CH 2 CH 3 .CH:CH.CH 3 

Normal or -butylene. /3-Butylene. Iso- or y-butylene. 

The isomerism of the first two compounds is due to a differ- 
ence in the position of the double binding, and it will be 
obvious, therefore, that the number of possible isomerides 
of any olefine which exhibits isomerism is greater than that 
of the corresponding paraffin. The three butylenes are all 
colourless gases, and combine directly with chlorine, bromine, 
hydrogen bromide, &c. 

Five isomeric amylenes or pentylenes, C 5 H 10 , are known, 
the most important being trimethylethylene or fi-iso-amylene, 

PTT v 

p 3 ^>C:CH-CH 3 , which is obtained by treating fusel oil 

3 

(pp. 100, 106) with zinc chloride; it is a colourless liquid, 
and boils at 32. 



HYDROCARBONS OF THE ETHYLENE SERIES 79 



SUMMARY AND EXTENSION. 

The Olefine or Ethylene Series. Unsaturated hydrocarbons 
of the general formula C n H 2n . The following are the more im- 
portant members of this series, the number of possible isomerides 
being given in brackets : 

Ethylene (1), C 2 H 4 Amylene (5), C 5 H 10 

Propylene (1), C 3 H 6 Hexylene (13), C 6 H 12 

Butylene (3), C 4 H 8 

Methods of Preparation. By the action of dehydrating agents, 
such as H 2 S0 4 , ZnCl 2 , P 2 5 , &c., on the alcohols (p. 89), 

CH 3 .CH 2 .OH = CH 2 : CH 2 + H 2 O. 

By the action of alcoholic potash on the alkyl halogen compounds 
(p. 174), 

CH 3 .CH 2 Br + KOH = CH 2 :CH 2 + KBr + H 2 O 
CH 3 .CHBr.CH 3 + KOH = CH 3 -CH :CH 2 + KBr + H 2 O. 

By the electrolysis of certain dibasic acids (p. 240), or, better, of 
their potassium salts, 

CH 2 .COOH CH 2 

! =11 +2C0 2 + H 2 . 

CH 2 -COOH CH 2 

Physical Properties. The first four members of the series are 
gases ; the following fourteen or so, liquids ; the higher members, 
solids at ordinary temperatures : the melting-point and the boiling- 
point rise on passing np the series, as in the case of the paraffins. 
They are insoluble, or nearly so, in water, but readily soluble in alcohol. 

Chemical Properties. The olefines burn with a luminous smoky 
flame, and can be exploded with oxygen or air. They are un- 
saturated hydrocarbons, and differ very considerably in chemical 
properties from the saturated hydrocarbons of the paraffin series ; 
whereas the latter are either not acted on, or form substitution 
products when treated with C1 2 , Br 2 , HC1, HBr, HC10, H 2 SO 4 , &c., 
the olefines, as a rule, readily enter into direct combination with 
all these substances, forming saturated additive products. 

The olefines are converted into paraffins on treatment with 
nascent hydrogen, 

CraH 2 n + 2H = CnH^n-f 2- 

They combine with chlorine and bromine, sometimes with iodine, 
forming saturated compounds which may be regarded as di-sub- 
stitution products of the paraffins, 

CH 3 .CH:CH 2 + C1 2 = CH 3 .CHC1.CH 2 C1. 



80 HYDROCARBONS OP THE ETHYLENE SERIES. 

They combine with hydrobromic and hydriodic acids, but not, as a 
rule, with hydrochloric acid, yielding alkyl halogen compounds, 



CH 2 :CH 2 + HBr = C 2 H 5 Br, 

combination generally taking place in such a manner that the 
halogen atom unites with that carbon atom which is combined with 
the smallest number of hydrogen atoms ; propylene, for example, 
yields with hydrobromic acid, isopropyl bromide, CH 3 -CHBr-CH 3 , 
and not propyl bromide, CH 3 -CH 2 -CH 2 Br ; normal butylene, 
CH 3 .CH 2 -CH:CH 2 , with hydriodic acid, gives secondary butyl 
iodide,* CH 3 .CH 2 .CHI.CH 3 , and so on. 

Fuming sulphuric acid, in some cases ordinary sulphuric acid, 
readily absorbs the olefines, forming alkyl hydrogen sulphates, 

CH 2 :CH 2 + H 2 SO 4 =CH 3 .CH 2 .SO 4 H. 

Hypochlorous acid, in aqueous solution, converts the olefines into 
chlorohydrins (p. 228). 

CH 2 :CH 2 + HOC1 = CH 2 C1.CH 2 .OH. 

Unlike the paraffins, the olefines are readily oxidised by chromic 
acid and by potassium permanganate. When oxidation is carried 
out carefully under suitable conditions, products containing the 
same number of carbon atoms as the original olefine are obtained ; 
ethylene, for example, giving ethylene glycol (p. 224) ; butylene, 
the corresponding butylene glycol, 

CH 2 :CH 2 + + H 2 = CH 2 (OH).CH 2 .OH 
CH 3 .CH 2 .CH: CH 2 + O + H 2 = CH 3 .CH 2 .CH(OH).CH 2 .OH. 
Generally speaking, when a substance contains the group 
CH = CH , this group, on oxidation, is in the first place con- 
verted into the group CH(OH)-CH(OH) . The compounds thus 
formed readily undergo further oxidation in such a way that the 
originally unsaturated carbon atoms become separated. Propylene, 
on vigorous oxidation, yields ultimately acetic and formic acids; 
ct-butylene gives propionic and formic acids, 



HYDROCARBONS OF THE ACETYLENE SERIES. 

The relation between the hydrocarbons of the acetylene 
series and those of the olefine series is similar to that between 
the olefines and the paraffins ; in other words, the members 
* Compare foot-note p. 265, 



HYDROCARBONS OF THE ACETYLENE SERIES. 81 

of the acetylene series contain two atoms of hydrogen less 
than the corresponding olefines, and the general formula of 
the series is C n H 2n _ 2 . 

Paraffins, C M H 2n+2 Olefines^ C n H 2 , t Acetylenes, C w H 2n _ 2 
Methane, CH 4 - 

Ethane, C 2 H 6 Ethylene, C 2 H 4 Acetylene, C 2 H 2 

Propane, C 3 H 8 Propylene, C 3 H 6 Allylene, C 3 H 4 

Butane, C 4 H 10 Butylene, C 4 H 8 Crotonylene, C 4 H 6 

Acetylene, C 2 H 2 , the simplest member of the series, occurs 
in small quantities (about 0-06 per cent, by vol.) in coal-gas. 
It is produced during the incomplete combustion of methane, 
ethyl alcohol, coal-gas, and other substances ; also when such 
substances are passed through a red-hot tube. It is formed 
when hydrogen is led through a globe in which the electric 
arc is passing between carbon poles (Berthelot), 



This synthesis of acetylene from its elements is of great 
interest, because ethylene can be produced from acetylene 
by the action of nascent hydrogen, and ethylene is readily 
converted into ethyl alcohol by treating with sulphuric acid 
and water consecutively (p. 94). As, moreover, a large 
number of organic substances can be produced from ethyl 
alcohol, it is possible to prepare all these compounds, starting 
with carbon and hydrogen. 

Acetylene is also produced when a solution of the potassium 
salt of fumaric acid (p, 247) undergoes electrolysis (Kekule), 
hydrogen being evolved at the negative pole, a mixture 
of acetylene and carbon dioxide at the positive pole (compare 
p. 72), 

C 2 H 2 (COOK) 2 = C 2 H 2 + 2C0 2 + 2K. 

Acetylene may be prepared by dropping ethylene dibromide 
into boiling alcoholic potash and collecting the gas over water 
(compare p. 73), 

C,H 4 Br 2 + 2KOH = C 2 H 2 + 2KBr + 2H 2 0. 

Or,. F^ 



82 HYDROCARBONS OF THE ACETYLENE SERIES. 

In the first place, the potash takes away one molecule* of 
hydrogen bromide (C 2 H 4 Br 2 + KOH = C 2 H 3 Br + KBr + H 2 0), 
and the vinyl bromide thus produced is then further acted on 
(C 2 H 3 Br + KOH - C 2 H 2 + KBr + H 2 0). 

A more convenient method of preparation is to burn 
coal-gas with a supply of oxygen insufficient for complete 
combustion. 

An ordinary Bunsen burner is lighted below, and an inverted glass 
funnel, connected by tubing with a Woulfe's bottle, is placed over 
it ; with the aid of a water-pump, or aspirator, the products are 
drawn through an ammoniacal solution of cuprous chloride, con- 
tained in the Woulfe's bottle, when the red copper derivative of 
acetylene is precipitated. This product is collected, washed with 
water, and warmed with hydrochloric acid, the liberated acetylene 
being collected over water. 

Acetylene is now prepared in the laboratory and also 
manufactured in large quantities from calcium carbide, a 
very hard, gray, crystalline substance, prepared by heating 
a mixture of calcium carbonate, or oxide, and coke at a 
very high temperature in an electric furnace, 



When calcium carbide is left exposed to the air it quickly 
absorbs moisture, and when placed in cold water it is 
rapidly decomposed with development of heat, acetylene 
being evolved, 

CaC 2 + 2H 2 = C 2 H 2 + Ca(OH) 2 . 

This reaction is made use of in the commercial preparation of 
the gas. 

For laboratory and lecture experiments a small lump of the 
carbide is placed under a gas-cylinder filled with, and inverted in, 
a vessel of water ; but if a stream of gas be required, the carbide is 
placed in a small flask containing a layer of sand and provided 
with a dropping funnel and delivery tube ; on allowing cold water 
to drop slowly on to the carbide a steady stream of gas is obtained. * 

* Commercial calcium carbide may contain calcium phosphide, and the 
acetylene obtained in this way may contain hydrogen phosphide (phosphiney 
as well as other impurities, 



HYDROCARBONS OP THE ACETYLENIS SERIES. 83 

Acetylene is a colourless gas, which liquefies at 1 under a 
pressure of 48 atmospheres. It has a characteristic smell, 
resembling that of garlic, and quite different from that which 
is noticed when a Bunsen is burning below, although the latter 
is often erroneously ascribed to the presence of acetylene. 
It is slightly soluble in water, much more readily in alcohol. 
Acetylene is a strongly endothermic compound, and can be 
detonated (with fulminate) under atmospheric pressure ; a 
mixture of acetylene and air or oxygen in suitable proportions 
explodes ivitJi great violence when ignited. When burnt in an 
open gas jar or from an ordinary flat-flame burner, acetylene 
gives a very smoky flame, this behaviour being shown, but 
to a less extent, by all hydrocarbons which contain a very 
large percentage of carbon ; when, however, specially con- 
structed burners are employed, smoking is prevented and 
the flame is almost dazzling in its brilliancy and very rich 
also in actinic rays (use in photography). 

Owing to the very high illuminating power of the acetylene flame, 
on the discovery of a cheap method of manufacturing calcium 
carbide, great expectations were formed that this gas would be the 
illuminating agent of the future ; hitherto, although acetylene is 
used alone in small quantities for such purposes (bicycle lamps), 
and in rapidly increasing quantities for enriching oil-gas (burnt 
principally in railway carriages), these high expectations have not 
been realised. This is due to the fact that acetylene is liable to 
explode when it is under a pressure of more than 30 Ibs. per square 
inch, and cannot therefore be safely stored in bottles or cylinders ; 
it should not be stored in metallic holders even under atmospheric 
pressure, as explosive metallic derivatives may be formed. 

Copper acetylide, C 2 Cu 2 , is a brownish-red amorphous com- 
pound which is precipitated when acetylene is passed into a 
solution of cuprous chloride in ammonia ; its formation serves 
as a delicate test for acetylene, and with the aid of this 
compound acetylene is easily separated from other gases. 
The dry substance explodes when struck on an anvil, or when 
heated at about 120. It is decomposed by Irydrochloric acid 
with formation of acetylene and traces of vinyl chloride, but 



84 HYDROCARBONS OF THE ACETYLENE SERIES. 

when warmed with a solution of potassium cyanide it yields 
pure acetylene. Silver acetylide, C 2 Ag 2 , is a colourless amor- 
phous compound, obtained on passing acetylene into an 
ammoniacal solution of silver nitrate. It is far more readily 
explosive than the copper compound, and detonates when 
gently rubbed with a glass-rod. 

When acetylene is passed over heated sodium or potassium, 
hydrogen is evolved, and a metallic substitution product 
formed, 

2C 2 H 2 + 2Na = 2C 2 HNa + H 2 . 

Potassium acetylide was first obtained by Davy in preparing 
potassium by heating together charcoal and calcined tartar (car- 
bonised hydrogen potassium tartrate) in an iron bottle ; he showed 
that this compound was decomposed by water giving a gas ' bicar- 
buret of hydrogen ' (acetylene) which burnt with a brilliant flame. 

Acetylene combines directly with nascent hydrogen, being 
converted first into ethylene (p. 72), then into ethane (p. 74), 

C 2 H 2 + 2H = C 2 H 4 C 2 H 2 + 4H = C 2 H 6 . 
It combines directly with chlorine in the light, forming 
probably dichlorethylene and tetrachlorethane, 

C 2 H 2 + C1 2 = C 2 H 2 C1 2 C 2 H 2 + 2C1 2 = C 2 H 2 C1 4 ; 
with bromine, forming dibromethylene and tetrabromethane, 
and with halogen acids under certain conditions, giving 
in the first place substitution products of ethylene. Thus, 
when the copper compound of acetylene is decomposed 
with hydrochloric acid, small quantities of vinyl chloride or 
chlorethylene are produced. 

Sulphuric acid absorbs acetylene. When the solution is 
diluted with water, and then distilled, acetaldehyde (p. 122) 
passes over, 



Acetaldehyde is also formed when acetylene is shaken with 
a warm aqueous solution of mercuric bromide, and the pre- 
cipitate then boiled with dilute sulphuric acid. 

This remarkable reaction that is, the addition of the elements of 
water to the group HC=CH, by treatment with-*sulphuric acid or 



i 



HYDROCARBONS OF THE ACETYLENE SERIES. 85 

vvitli halogen mercuric salts appears to be a general one, and 
is frequently employed as a method of synthesis in organic 
investigations. 

When acetylene is heated at a dull red heat, it is converted 
into benzene (Part II. p. 311), 

3C 2 H 2 = C 6 H 6 . 

Constitution of Acetylene. The formation of acetylene from 
ethylene dibromide may be expressed by the equation, 
H H 

H-C-C-H = C 2 H 2 + 2HBr, 

Br Br 

so that the constitution of the hydrocarbon might be repre- 
sented by one of the formulae, 

H H H 

C C H-C-C, 

which, in order to recall the fact that carbon is tetravalent, 
and that acetylene combines directly with four monad atoms, 
must then be written, 

H H H 

-C-C- or H-C-C-. 
II II 

i. ii. 

Since, however, as stated in discussing the constitution of 
ethylene, one unsaturated carbon atom is never found to exist 
alone, but requires the presence of another, it must be assumed 
that the particular portion of the combining capacity of each of 
the carbon atoms which is not exerted in uniting with hydro- 
gen, is in some way exerted in combining with or satisfying 
the other carbon atom. For these reasons, formula i. is written, 
H H 

c=c or CH;CH. 

But it is impossible to write formula n. in any such manner, 
and at the same time to represent both carbon atoms as 
actively tetravalent. For these and other reasons the con- 



86 HYDROCARBONS OF THE ACETYLENE SERIES. 

stitution of acetylene is expressed by the formula CHiCH, 
which recalls the fact that it contains doubly unsaturated 
carbon atoms, and is capable of combining directly with 
two pairs of monad groups or atoms to form additive 
compounds. This view of the constitution of acetylene 
accords well with its whole chemical behaviour. 

The formation of acetylene by the electrolysis of fumaric acid 
affords support to this view, as will be readily understood if the 
decomposition be represented thus : 

CH COOH CH C0 2 H CH 

= 1 + + =111 +2CO 2 + H 2 . 
CH COOH CH CO 2 H CH 

Fumaric Acid. 

When the hydrocarbon combines with two monovalent 
atoms, such as 2H, C1 2 , Br 2 , HBr, &c., it loses part of its 
unsaturated character, and the two carbon atoms, which 
before were represented as joined by three lines, or by a 
treble binding or treble linking, are now represented as 
joined by two only, as in the defines, 

CH i CH + 2H = CH 2 :CH 2 CH 1 CH + Br 2 = CHBr:CHBr. 

If, now, these compounds, which are still unsaturated, again 
combine with 2H, Br 2 , &c., they are converted into saturated 
compounds, 

CH 2 :CH 2 + 2H = CH 3 -CH 3 
CHBr:CHBr + Br 2 = CHBr 2 .CHBr 2 . 

Acetylene can also combine with the valency equivalent of 
four monad atoms, with one atom of oxygen and two atoms 
of hydrogen, for example, 

CH H H CH 3 

I + V = I 
;H o H c=o 



Two hydrocarbons of the molecular formula C 3 H 4 are 
known ; they may be represented by the formulse, 
CH 3 .C!CH and CH 2 :C:CH 2 . 

Allyleue or Methylacetyleue. Alleue. 



HYDROCARBONS OF THE ACETYLENE SERIES. 87 

Allylene, like acetylene, contains two doubly unsaturated 
carbon atoms, whereas allene resembles rather ethylene in 
constitution, and may be considered as containing two pairs 

of singly unsaturated carbon atoms, CH 2 :C:CH 2 ; the latter, 

therefore, is not a homologue of acetylene, but belongs to 
the cli-olefine series (see below). This example shows that, 
in the case of unsaturated hydrocarbons, isomerism may 
occur even when the carbon ' skeleton ' or framework is the 
same, not only because the relative positions of the double 
linkings may be different (p. 78), but also because there 
may be a difference in the extent of unsaturation of a par- 
ticular carbon atom ; consequently the number of possible 
isomerides in any given case is even greater in the C M H 2n _ 2 
than in the olefine series. 

Allylene, or methylacetylene, CH 3 -C:CH, is prepared by heat- 
ing propylene dibromide (dibromopropane) with alcoholic potash, 

CH 3 .CHBr.CH 2 Br + 2KOH = CH 3 -C i CH + 2KBr + 2H 2 O. 
It is a gas, very similar to acetylene in properties, and gives 
characteristic copper and silver compounds. 

Crotonylene, or dimethylacetylene, CH 3 -C:C-CH 3 , prepared 
by warming the dibromide of /3-butylene (p. 78) with alcoholic 
potash, 



is a liquid boiling at 27-28 ; it does not form copper or silver de- 
rivatives with ammoniacal solutions of cuprous chloride or silver 
nitrate, as this property is only shown by those hydrocarbons 
which contain the group -C:CH. 

Diallyl, CH 2 :CH.CH 2 .CH 2 .CH:CH 2 , is a hydrocarbon of the di- 
olefine series, of which allene (see above) is the first member. 
Diallyl is a liquid (b.p. 59), prepared by warming allyl iodide 
(p. 261) with sodium, 

2CH 2 :CH.CIU + 2Na = CH 2 :CH.CH 2 .CH 2 .CH:CH 2 + 2NaI. 

It combines directly with two molecules of bromine yielding 
diallyl tetrabromide, which, when dropped into hot alcoholic 
potash, is converted into dipropargyl, 

CHoBr.CHBr.CHo-CH 2 .CHBi-.CH 2 Br + 4KOH- 
" CH ; C.CH 2 .CH 2 -C i CH + 4KBr + 4H 2 O. 



88 HYDROCARBONS OF THE ACETYLENE SERIES. 

Dipropargyl is an important member of the di-acetylene series ; it 
is a liquid boiling at 85, and resembles acetylene in forming copper 
and silver derivatives. 

SUMMARY AND EXTENSION. 

The hydrocarbons, C n H 2n _ 2 , may be classed in two groups : 
(1) The true acetylene series, consisting of those compounds 
which, like acetylene, contain the group C ! C ; and (2) the 
di-olefines, or hydrocarbons, such as allene, CH 2 :C:CH 2 , and 
diallyl, CH 2 :CH.CH 2 .CH 2 .CH:CH 2 , which resemble the olefines 
in constitution. The former behave on the whole like acetylene, 
whereas the latter are similar to the olefines. 

The Acetylene Series : Unsaturated hydrocarbons of the 
general formula C n H2 M -2- The most important members of this 
series are acetylene, CHlCH ; allylene, CH 3 -C:CH ; and crotonylene, 
CH 3 .C;C.CH 3 . 

Methods of Preparation. By treating the monohalogen substitu- 
tion products of the olefines, or the dihalogen substitution products 
of the paraffins, with alcoholic potash, 

CH 2 :CHBr + KOH = CH ; CH + KBr + H 2 
CH 3 .CHBr.CH 2 Br + 2KOH = CH 3 -C CH + 2KBr + 2H 2 0. 

By tlie electrolysis of the alkali salts of unsaturated dibasic acids, 

CH-COOH CH 

+ 2C0 2 + H 2 . 



Je. 



COOH CH 

Physical and Chemical Properties. The members of the acetylene 
series up to C 12 H 22 are gases or volatile liquids having a peculiar 
odour. They are sparingly soluble in water, more readily in 
alcohol, and burn with a luminous, very smoky flame. 

Those hydrocarbons of the true acetylene series which contain 
the group -CiCH form metallic compounds such as copper acetylide, 
C 2 Cu 2 , and silver acetylide, C 2 Ag 2 , when treated with ammoniacal 
solutions of cuprous chloride and silver nitrate. The copper com- 
pounds are red, the silver compounds white, and both classes are 
explosive, the latter more so than the former. These compounds 
are decomposed by hydrochloric acid, and by warm potassium 
cyanide solution, the acetylenes being regenerated. The di- 
olefines, and those members of the true acetylene series, such as 
CH 3 -C:C'CH 3 , which do not contain the group CiCH, do not 
form these metallic derivatives. 

The hydrocarbons of the true acetylene series may be caused 



HYDROCARBONS OP THE ACETYLENE SERIES. 89 

to combine with the elements of water by dissolving them in strong 
sulphuric acid, and then adding water and warming ; or by shaking 
them with a concentrated aqueous solution of mercuric chloride 
or bromide, and then decomposing the precipitate which is formed 
with a dilute mineral acid ; or by merely heating them with water 
at 325, 



In the case of all the higher members, combination takes place 
in such a way that the oxygen atom becomes united with the 
carbon atom which is not combined with hydrogen ; allylene, for 
example, yields acetone, as shown above, and not propaldehyde, 
CH 3 -CH 2 .CHO. 

All the hydrocarbons of the CH 2n _ 2 series combine directly with 
two molecules of chlorine, bromine, halogen acids, and with nascent 
hydrogen, &c., the action taking place in two stages, 
C 2 H 2 + 2H = C.,H 4 C 2 H 2 + 4H = C H 6 

CH 3 -C i CH + Br 2 = CH 3 -CBr:CHBr 



Like the defines, they are readily oxidised and finally converted 
into compounds containing a smaller number of carbon atoms in 
the molecule. 



CHAPTEE VI. 

THE MONOHYDRIC ALCOHOLS. 

The monohydric alcohols form a homologous series of the 
general formula C n H 2n+1 -OH, or C n H 2n+2 0. They may be 
regarded as derived from the paraffins by the substitution 
of the monovalent hydroxyl-group HO- for one atom of 
hydrogen. 

Methyl alcohol, CH 8 -OH, derived from methane, CH 3 -H 
Ethyl C 2 H 5 -OH, ,. ethane, C 2 H 5 -H 

Propyl M C 3 H r OH, propane, C 3 H r H, &c. 

Methyl alcohol, 'wood-spirit, or carbinol, CH 3 -OH, occurs in 
nature in several substances, amongst others in combination 
with salicylic acid, as methyl salicylate, in oil of winter- 
green (Gaultheria procumbens). When this oil is distilled 



90 THE MONOHYDRIC ALCOHOLS. 

with dilute potash, an aqueous solution of pure methyl 
alcohol collects in the receiver. Methyl alcohol may be 
obtained from methane, by first converting the hydrocarbon 
into methyl chloride, and then heating the latter with dilute 
aqueous potash in closed vessels, 

CH 3 C1 + KOH = CH 3 -OH + KC1. 

Methyl alcohol is prepared from the products of the 
destructive distillation of wood. When wood is heated in 
iron retorts out of contact with air, gases are evolved ; water, 
methyl alcohol, acetic acid, tar, and other products collect in 
the receiver ; and wood-coke or charcoal remains. 

After allowing the distillate to settle, the brown aqueous layer, 
which contains methyl alcohol, acetic acid, acetone, and other sub- 
stances, is drawn off from the wood-tar and distilled from a copper 
vessel, the vapours being passed through hot milk of lime, to free 
them from acetic acid, and then collected in a receiver ; this dis- 
tillate is first diluted with water, when hydrocarbons and other oily 
impurities which are insoluble in the dilute alcohol are thrown out 
of solution ; after filtering through charcoal or separating the oily 
layer which collects at the surface on standing, the liquid is next 
submitted to fractional distillation, finally over quicklime, until it 
contains 98-99 per cent, of methyl alcohol. In order to free it from 
acetone and other impurities, it is mixed with powdered calcium 
chloride, with which the methyl alcohol combines, forming a 
crystalline compound of the composition CaCl 2 + 4CH 4 O. This 
substance is freed from acetone by gently heating it or by pressing 
it between cloths, and is then decomposed by distilling with water ; 
the aqueous methyl alcohol is finally dehydrated by repeated 
distillation with quicklime, but it still contains traces of acetone 
and other impurities. 

Pure methyl alcohol can be prepared by warming the 
impure compound with anhydrous oxalic acid, when methyl 
oxalate is produced (p. 238), 

2CH 3 .OH + C 2 4 H 2 = C 2 4 (CH 3 ) 2 + 2H 2 ; 
this crystalline substance is drained on a filter pump, de- 
composed by distilling with potash, and the aqueous solution 
of pure methyl alcohol is then freed from water by distilling 
it with quicklime. 



THE MONOHYDRIC ALCOHOLS. 91 

Methyl alcohol is a colourless, mobile liquid of sp. gr. 
0-796 at 20; it boils at 66, and has an agreeable vinous or 
wine-like odour and a burning taste. It mixes with water in 
all proportions, a slight contraction in volume taking place, 
and heat being developed ; it burns with a pale, non-luminous 
flame, and its vapour forms an explosive mixture with air or 
oxygen, 

2CH 3 .OH + 30 2 = 2C0 2 + 4H 2 0. 

It is largely used in the manufacture of organic dyes and 
varnishes, and for the preparation of methylated spirit 
(p. 101). 

Sodium and potassium dissolve readily in methyl alcohol 
with evolution of hydrogen and formation of metallic 
compounds called methylates or methoxides, 

2CH 3 .OH + 2Na = 2CH 3 -ONa + H 2 , 

a reaction which is similar to the decomposition of water 
by sodium. Sodium methoxide is readily soluble in methyl 
alcohol, but can be obtained in a solid condition by evaporat- 
ing the solution in a stream of hydrogen \ it is a colourless, 
crystalline, very deliquescent compound, which rapidly absorbs 
carbon dioxide from the air, and is immediately decomposed 
by water with regeneration of methyl alcohol, 

CH 3 .ONa + H 2 = CH 3 -OH + NaOH. 
potassium methoxide has similar properties. 

Although neutral to test-paper, methyl Ulcohol acts like a 
weak base, and combines with acids to form salts ; when 
saturated with hydrogen chloride it yields methyl chloride, 
corresponding with potassium chloride, 

CH 3 .OH + HC1 = CH 3 C1 + H 2 



and when warmed with sulphuric acid it gives methyl 
hydrogen sulphate, corresponding with potassium hydrogen 
sulphate, and very small quantities of methyl sulphate, cor- 
responding with potassium sulphate, 



92 THE MONOHYDRIC ALCOHOLS. 

CH 3 -OH + H 2 S0 4 = CH 3 -HS0 4 + H 2 

2CH 3 -OH + H 2 S0 4 = (CH 3 ) 2 S0 4 + 2H 2 0. 

When phosphorus pentachloride, trichloride, or oxychloride 

is added to methyl alcohol, a considerable development of 

heat occurs, and methyl chloride is formed, 

CHg-OH + PC1 5 - CH 3 C1 + HC1 + POC1 3 
3CH 3 -OH + PC1 3 = 3CH 3 C1 + H 3 P0 3 * 
3CH 3 .OH + POC1 3 = 3CH 3 C1 + H 3 P0 4 .* 
The corresponding bromides of phosphorus act in a similar 
manner. 

Methyl alcohol is readily oxidised,! being first converted 

* These reactions only take place to a small extent ; the principal products 
are eaters of phosphorous or phosphoric acid, 

3CH 3 -OH +PC1 3 =P(OCH 3 ) 3 + 3HC1 
3CH 3 -OH + POC1 3 = PO( OCH 3 ) 3 + 3HC1. 

f The substances frequently used in oxidising organic compounds are : 
Chlorine water, bromine water, nitric acid, chromic acid, manganese 
dioxide and sulphuric acid, and potassium permanganate. 
Chlorine and bromine, in presence of water, supply oxygen, 

Cl2+H 2 O=2HCl + 0. 

Nitric acid gives up some of its oxygen and is reduced to an oxide of 
nitrogen, the nature of which depends on that of the substance undergoing 
oxidation, and on the conditions of the experiment, 

2HNO 3 = H 2 O + N 2 3 + 2O 2HNO 3 = H 2 O + 2NO 2 + O, &c. 
Chromic acid in the presence of sulphuric or acetic acid gives oxygen and 
a chromic salt, 

2CrO 3 =Cr 2 O 3 +3O, or 2CrO 3 +3H 2 SO 4 =Cr 2 (S0 4 ) 3 + 3H 2 O + 3O. 
A mixture of potassium dichromate and sulphuric acid, which is very often 
used instead of chromic acid, yields oxygen and a mixture of chromic 
sulphate and potassium sulphate, which frequently crystallises out in dark 
purple octahedra of chrome-alum, K 2 SO 4 , Cr 2 (SO 4 ) 3 + 24H 2 O, 

K 2 Cr 2 7 + 4H 2 SO 4 = K 2 S0 4 + Cr 2 (SO 4 ) 3 + 4H 2 O + 3O. 

Potassium permanganate, in alkaline solution, is decomposed, yielding a 
precipitate of hydrated manganese dioxide, 

2KMnO 4 + H 2 O = 2MnO 2 + 2KOH + 3O ; 

but in acid solution the same quantity of permanganate gives five instead 
of three atoms of oxygen, 

2KMn0 4 + 3H 2 SO 4 =K2SO 4 + 2MnSO 4 + 3H 2 O -f- 50, 
because manganese dioxide and sulphuric acid yield oxygen, 
MnO 2 +H 2 SO 4 =MnSO 4 



THE MONOHYDBIC ALCOHOLS. 93 

into formaldehyde and then into formic acid, 

CH 3 .OH + = CH 2 + H 2 CH 2 + = CH 2 2 . 

Formaldehyde. Formic Acid, 

Constitution of Methyl Alcohol. Since only one of the 
four hydrogen atoms in methyl alcohol, CH 4 0, is displaceable 
by potassium or sodium, it must be concluded that this 
particular hydrogen atom is in a different state of combina- 
tion from the other three ; but methyl alcohol is formed by 
the action of dilute alkalies on methyl chloride, 

CH 3 C1 + KOH = CH 3 -OH + KC1, 

and th*- three hydrogen atoms in methyl chloride, which are 
known to be combined with carbon, are not displaceable 
by metals. It is evident, therefore, that the displaceable 
hydrogen atom in methyl alcohol is not combined with 
carbon; the only other possibility is that it is combined 
with oxygen, and that methyl alcohol has the constitution 
H 

H-C-0 H, which is usually written CH 3 -OH. When 
H 

represented in this way, the whole chemical behaviour of 
methyl alcohol is summarised in its graphic formula; the fact 
that the oxygen atom cannot be taken away without one of 
the hydrogen atoms accompanying it as, for example, when 
the alcohol is treated with HC1, PC1 5 , PBr 5 , &c. is recalled 
by the two atoms being represented as directly united. The 
similarity between methyl alcohol and the metallic hydroxides 
is also accounted for ; the alcohol may be regarded as derived 
from water, H-O-H, by substituting the monovalent CH 3 - 
group for one atom of hydrogen, just as sodium hydroxide, 
Xa-OH, is obtained by the substitution of one atom of 
sodium. Methyl alcohol, in fact, is methyl hydroxide, and, 
like other hydroxides, it forms salts and water when treated 
with acids (p. 174), 



94 THE MONOHYDRIC ALCOHOLS. 

CH 3 .OH + HC1 - CH 3 C1 + H 2 
Na-OH + HC1 - IS T aCl + H 2 0. 

Like water and certain metallic hydroxides, it contains dis- 
placeable hydrogen, 



Zn(OH) 2 + 2KOH = Zn(OK) 2 + 2H 2 0. 

It may also be considered as a hydroxy-substitution product 
of the paraffin, methane ; it is termed a monohydric alcohol 
because it contains one hydroxyl-group. 

Ethyl alcohol, spirit of wine, alcohol, or methyl carbinol, 
C 2 H 5 -OH, has been known from the earliest times, as it is 
contained in all fermented liquors ; it occurs in plants in com- 
bination with organic acids. 

It may be obtained from ethane by converting the hydro- 
carbon into ethyl chloride and heating the latter with dilute 
alkalies under pressure, 

C 2 H 5 C1 + KOH = C 2 H 5 .OH + KC1, 

and by passing ethylene into fuming sulphuric acid, and then 
boiling the solution of ethyl hydrogen sulphate with water, 
a reaction of considerable theoretical importance, 

C 2 H 4 + H 2 S0 4 = C 2 H 5 -HS0 4 
C 2 H 5 -HS0 4 + H 2 - C 2 H 5 -OH + H 2 S0 4 ; 

also by reducing acetaldehyde in aqueous solution with sodium 
amalgam and water, 



Alcohol is prepared byplacing aweak (5-10 per cent.)aqueous 
solution of cane- or grape-sugar in a capacious flask, adding a 
.small quantity of brewer's yeast, and keeping the mixture in 
a warm place (at about 20). After some time it begins to 
froth and ferment (p. 97), and, if the flask be fitted with a 
cork and delivery tube, it can be proved that carbon dioxide 
is being evolved by passing the gas into lime-water. After 
about twenty-four hours' time the yeast is filtered off, and 



THE MONOHYDRIC ALCOHOLS. 95 

the solution distilled from a flask or retort connected with 
a condenser, the process being stopped when about one-third 
has passed over. In this way the more volatile alcohol is 
partially separated from the water (fractional distillation). 
The distillate has a peculiar vinous smell, and consists of 
an aqueous solution of slightly impure alcohol. It is poured 
into a retort or flask connected with a condenser, and a con- 
siderable quantity of freshly burnt lime in the form of small 
lumps is then slowly added ; after some hours, the alcohol is 
distilled by heating on a water-bath. By repeating this pro- 
cess several times, employing fresh caustic lime in sufficient 
quantity, alcohol containing only about 0-2 per cent, of water 
is obtained, but it is impossible to free it completely from 
water by distillation over lime. When the alcohol contains 
less than about 0-5 per cent, of water, it is known commer- 
cially as absolute alcohol. 

Wines, beers, and spirits contain alcohol, and its prepara- 
tion from these liquids is very simple. The liquid is distilled, 
and the alcohol, thus freed from colouring matter and other 
solid substances, is then dehydrated by distillation with 
caustic lime ; it still contains traces of volatile impurities. 

Alcohol is a colourless, mobile liquid of sp. gr. 0-8062 at 0; 
it has a pleasant vinous odour and a burning taste ; it boils 
at 78, but does not solidify until about - 130 (hence its 
use in alcohol thermometers). It burns with a pale, non- 
luminous flame, and its vapour forms an explosive mixture 
with air or oxygen, 

C 2 H 5 .OH + 30 2 = 2C0 2 + 3H 2 0. 

It mixes with water in all proportions with development 
of heat and diminution of volume; 52 vols. of alcohol and 
48 vols. of water give a mixture occupying only 96-3 vols. 

Ethyl alcohol closely resembles methyl alcohol in chemical 
properties. It quickly dissolves sodium arid potassium with 
evolution of hydrogen and formation of ethylates or ethoxides, 

2C 2 H 5 .OH + 2Na = 2C 2 



96 THE MONOHYDRIC ALCOHOLS. 

These compounds are readily soluble in alcohol, but may be 
obtained in a solid condition by evaporating the solution 
in a stream of hydrogen. They are colourless, hygroscopic 
substances, rapidly absorb carbon dioxide from the air, and 
are immediately decomposed by water with regeneration of 
alcohol, 

C 2 H 5 .OK + H 2 = C 2 H 5 .OH + KOH. 

Although it has a neutral reaction, alcohol acts like a weak 
base, and when treated with acids, is converted into salts with 
formation of water, 

C 2 H 5 .OH + HI = C 2 H 5 I + H 2 0. 

When treated with the chlorides or bromides of phosphorus, 
it is converted into ethyl chloride or ethyl bromide, an 
energetic action taking place (compare p. 92), 

C 2 H 5 -OH + PBr 5 - C 2 H 5 Br + HBr + POBr 3 . 

Alcohol is readily oxidised by chromic acid, yielding acetalde- 
hyde, which on further oxidation is converted into acetic 
acid, 

C 2 H 5 . OH + = C 2 H 4 + H 2 C 2 H 4 + = C 2 H 4 2 . 

Acetaldehyde. Acetic Acid. 

By the action of the ferment, mycoderma aceti, it is, under 
certain conditions (p. 150), oxidised to acetic acid at ordinary 
temperatures by the oxygen of the air. 

The presence of alcohol in aqueous solution may be detected 
by Lieben's iodoform reaction (p. 178). A small quantity of 
iodine is placed in the solution, and after warming gently potash 
is added drop by drop until the colour of the iodine disappears.' 
If alcohol be present in considerable quantity, a yellow pre- 
cipitate of iodoform is produced almost immediately. In 
very dilute solutions of alcohol only a very slight precipi-' 
tate is formed even after some time, but it may be recognised 
as iodoform by its odour, and by the characteristic appearance 
of its six-sided crystals when viewed under the microscope. 
By means of this reaction it is possible to detect 1 part of 



THE MONOHYDRIC ALCOHOLS. 97 

alcohol in 2000 parts of water. It is especially valuable 
as affording a means of distinguishing between ethyl and 
methyl alcohols, as the latter does not give the iodoform 
reaction, although many other substances, such as acetone, 
aldehyde, &c., do so. 

The presence of water in alcohol can be detected by adding 
a little anhydrous copper sulphate. If water be present, the 
colourless powder turns blue, owing to the formation of the 
hydrated salt, but this test is not very delicate. 

Constitution. The formation of alcohol from ethyl chloride, 
the fact that only one of its six atoms of hydrogen is dis- 
placeable by metals, and its close resemblance to methyl 
alcohol in chemical properties, lead to the conclusion that 

H H 

it is a hydroxide of the constitution H C C O H, or 

H i 

C 2 H 5 -OH. It may be regarded as a monohydroxy-sub- 
stitution product of ethane. 

Production of Wines and Beers ; Alcoholic Fermentation. 

When the juice of grapes is kept for a few days at 
ordinary temperatures, it changes into wine ; the sugars, 
glucose and fructose (p. 267), present in the juice being 
decomposed into alcohol and carbon dioxide. This change 
is brought about by a small vegetable organism ; the process 
is called fermentation, and the active agent which causes the 
change is termed a ferment. All wines, beers, and spirits, and 
the whole of the alcohol of commerce, are prepared by the 
process of fermentation. 

The ferment which brings about the conversion of grape- 
juice into wine is present on the grapes and stalks and in 
the air ; it is a living organism, and during fermentation 
it rapidly grows and multiplies, feeding on the sugar, mineral 
salts, and nitrogenous substances contained in the juice. In 
order that fermentation may take place, the conditions must 

Org. G 



98 THE MONOHYDRIC ALCOHOLS. 

be favourable to the life and growth of the living ferment ; 
sufficient food of a suitable kind must be at hand, and the 
temperature must be within certain limits. 

Beer is prepared from malt and hops. Malt is the grain 
of barley which has been caused to sprout or germinate by 
first soaking it in water and then keeping it in a moist 
atmosphere at a suitable temperature. During the process 
of germination diastase (p. 99) is formed in the grain. 
The malt is now heated at 50-100 in order to stop germina- 
tion and to cause the production of various substances which 
impart to it both colour and flavour, the character of the 
beer depending largely on the temperature and the duration 
of heating. It is then stirred up with water and kept at 
60-65, when fermentation sets in, the diastase converting 
the starch in the malt into dextrin and a sugar, maltose. 
The solution ('wort') is now boiled in order to stop the 
diastatic fermentation, and hops, the flower of the hop-plant, 
are added in order to impart a slight bitter taste, and also on 
account of the preservative properties of the hops. After 
cooling to from 5 to 20, yeast is added, when alcoholic fer- 
mentation sets in, the sugar maltose being gradually converted 
into alcohol and carbon dioxide. The beer is then run off 
and kept until ready for consumption. 

Beer usually contains 3-6 per cent, of alcohol, small 
quantities of dextrin, sugars, and colouring matters, and 
traces of succinic acid, glycerol, and other substances. It 
contains, moreover, carbon dioxide, to which it owes its 
refreshing taste, and small quantities of fusel oil, which help 
to give it a flavour. 

The production of beer involves two distinct fermentations. In 
the first place, the starch in the malt is converted into maltose and 
dextrin by the diastase, 

3(C 6 H 10 5 ) + H 2 = C ls H n O u + C 6 H 10 5 ; 

Starch. Maltose. Dextrin. 

in the second place, the maltose is transformed into alcohol by the 
yeast, 

C 12 H 22 O n + H 2 - 4C 2 H 6 + 4C0 2 . 



THE MONOHYDRIO ALCOHOLS. 



99 



One of the ferments cannot do the work of the other ; yeast cannot 
convert starch into maltose, nor can diastase set up the alcoholic 
fermentation of sugar. Diastase is an amorphous substance, 
without definite form or structure, and apparently lifeless. Such 
ferments are termed enzymes, in contradistinction to living organ- 
ised ferments of definite structure, of which yeast is an example.* 

Yeast (saccharomyces) consists of rounded, almost trans- 
parent living cells about 0-01 mm. in diameter, which are 
usually grouped together in chain-like clusters ; when magni- 
fied (350 diameters), yeast cells have the appearance shown 
in figs. 18 and 19.t When placed in solutions of certain 





Fig. 18. Burton Yeast. 



Fig. 19. London Yeast. 



sugars containing small quantities of mineral substances, &c., 
which the organism requires for food, the cells soon begin to 
bud and multiply, provided also that the temperature is kept 
between about 5 and 30; if it exceed these limits the 
plant stops growing, and fermentation ceases. 

There are several sugars which can be fermented with yeast, 
the most important being glucose or grape-sugar, C 6 H 12 6 , 
fructose or fruit-sugar, C 6 H 12 6 , and maltose, C ]2 H 22 O n . 

* Recent experiments seem to show that the action of yeast is due to 
an enzyme (zymase) contained in the cells, and that fermentation can be 
brought about by the juice of the cells in absence of the living organism 
(Buclmer). 

f From The Microscope in the Brewery. 



100 THE MONOHYDRIC ALCOHOLS. 

Sucrose or cane-sugar, C 12 H 22 O n , does not ferment with pure 
yeast, but does so with ordinary yeast, because the latter 
contains an enzyme (invertase) which rapidly converts the 
sucrose into equal molecules of glucose and fructose, 

C 12 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 . 

Sucrose. Glucose. Fructose. 

The alcoholic fermentation of these sugars is expressed 
approximately by the equation, 



but small quantities of fusel oil, glycerol, succinic acid, and 
other substances are also formed. Fusel oil (p. 106) is a 
variable mixture of the higher homologues of ethyl alcohol ; 
it is usually present in small quantities in beers and spirits. 

Manufacture of Alcohol and Spirits. Alcohol is prepared on 
the large scale from potatoes, grain, rice, and other substances 
rich in starch. The raw material is reduced to a pulp or paste 
with water, mixed with a little malt, and the mixture kept 
at about 60 for 30-60 minutes, when diastatic fermentation 
takes place, and the starch is converted into dextrin and 
maltose. After cooling to about 15, yeast is added, and 
the mixture kept until alcoholic fermentation is at an end. 
It is possible to obtain alcohol from starch without the 
use of malt, since starch is converted into glucose when 
heated with dilute sulphuric acid, and, after neutralising 
with lime, the solution can be fermented with yeast. Alcohol 
is also prepared from beetroot, molasses (treacle), and other 
substances rich in sugar, by direct fermentation with yeast. 

The weak solution of alcohol obtained by any of these 
methods is submitted to fractional distillation in specially 
constructed apparatus. The distillate is known as ' raw spirit,' 
and contains from 80-95 per cent, of alcohol and a small 
quantity of fusel oil, which passes over in spite of the fact 
that its constituents boil at a higher temperature than does 
alcohol or water. 

For the preparation of spirits, liqueurs, and other articles 



THE MONOHYDRIC ALCOHOLS. 101 

of consumption, the raw spirit must be freed as much as 
possible from fusel oil, which is very injurious to health. 
For this purpose it is diluted with water and filtered through 
charcoal, which absorbs some of the fusel oil. Finally, the 
spirit is again fractionally distilled, the portions which pass 
over first (' first runnings') and last ('last runnings ') being 
collected separately ; the intermediate portions consist of 
'refined' or 'rectified spirit,' most of the fusel oil, which 
has not been removed, being present in the last runnings. 

For most other purposes the separation of the fusel oil 
is unnecessary, and if a stronger alcohol be required, the raw 
spirit is again fractionated, or distilled over quicklime. 

Alcohol is used in large quantities for the manufacture of 
ether, chloroform, &c., and in the purification of the alkaloids. 
It is employed as a solvent for gums, resins, and other sub- 
stances, in the preparation of tinctures, varnishes, perfumes, 
&c., and is also used in spirit-lamps. In this country a 
heavy excise duty has long been levied on spirit of wine, a 
fact which acted as a serious impediment to its extended use ; 
but since 1856 the Government has permitted the manufacture 
and sale of methylated spirit free of duty. 

Methylated spirit contains about 90 per cent, of raw spirit 
(aqueous ethyl alcohol), about 10 per cent, of partially purified 
wood-spirit or methyl alcohol, and a small quantity of paraffin- 
oil, the addition of which renders the alcohol unfit for drinking 
purposes, without greatly affecting its value as a solvent; 
methylated spirit is therefore used instead of alcohol when- 
ever possible, as it is so much cheaper. Methylated spirit 
cannot be separated into its constituents by any commercial 
process, but the water and tarry impurities can be got rid of 
almost completely by distilling with strong potash, and then 
dehydrating over lime ; the purified spirit may be employed 
in some chemical experiments in the place of pure ethyl 
alcohol, but its purification is troublesome and wasteful. 

Alcdholometry. In order to ascertain the strength of a 
sample of alcohol that is, the percentage of alcohol in pure 



102 THE MONOHYDRIO ALCOHOLS. 

aqueous spirit, it is only necessary to determine its specific 
gravity at some particular temperature, and then to refer to 
published tables, in which the sp. gr. of all mixtures of 
alcohol and water is given. If, for example, the sp. gr. is 
found to be 0-8605 at 15-5, reference to the tables would 
show that the sample contained 75 per cent, of alcohol by 
weight. 

For excise and general purposes the sp. gr. is determined 
with the aid of hydrometers graduated in such a manner 
that the percentage of alcohol can be read off directly on the 
scale. The standard referred to in this country is proof-spirit, 
which contains 49-3 per cent, by weight, or 57-1 per cent, 
by volume of alcohol ; it is defined by act of Parliament as 
being ' such a spirit as shall at a temperature of 51 F. weigh 
exactly ^fths of an equal measure of distilled water.' Spirits 
are termed under or over proof according as they are weaker 
or stronger than proof-spirit : thus 20 over proof means 
that 100 vols. of this spirit diluted with water would yield 
120 vols. of proof -spirit, whilst 20 under proof means that 
100 vols. of the sample contain as much alcohol as 80 vols. 
of proof -spirit. The name proof-spirit owes its origin to 
the ancient practice of testing the strength of samples of 
alcohol by pouring them on to gunpowder and applying a 
light. If the sample contained much water, the alcohol 
burned away, and the water made the powder so damp that 
it did not ignite ; but if the spirit were strong enough, the 
gunpowder took fire. A sample which just succeeded in 
igniting the powder was called proof-spirit. 

For the determination of alcohol in beers, wines, and spirits, 
a measured quantity of the sample is distilled from a flask con- 
nected with a condenser until about one-third has passed over. 
The distillate, which contains the whole of the alcohol, is then 
diluted with water to the volume of the sample taken, and 
its sp. gr. determined with a hydrometer ; the percentage of 
alcohol is found by referring to the tables already mentioned. 
.Distillation is necessary because the sugary and other 



THE MONOHYDRTC ALCOHOLS. 103 

extractive matters contained in the sample influence the 
sp. gr. to such an extent that a direct observation would be 
of no value. 

The percentage of alcohol by weight in some of the best- 
known fermented liquors may be taken as being roughly as 
follows : 

Brandy 50% Port 20% Claret 7% 

Whisky 50 % Sherry 16 % Burton Ale . . 5-5 % 

Gin 40% Hock 8% Lager-beer 3% 

Homologues of Ethyl Alcohol. The members of the series 
of monohydric alcohols may all be considered as derived from 
the paraffins by the substitution of the monovalent HO- 
group for one atom of hydrogen. Like the paraffins, they 
exist in isomeric forms, but, as two or more isomeric alcohols 
may be derived from one hydrocarbon, the number of iso- 
merides is greater in the alcohol than in the paraffin series. 
Propane, CH 3 -CH 2 -CH 3 , for example, exists in only one 
form, but two isomeric alcohols may be derived from it 
namely, propyl alcohol, CH 3 -CH 2 -CH 2 -OH, and isopropyl 
alcohol, CH 3 .CH.CH 3 , or CH 3 .CH(OH)-CH 3 . 

OH 

In order to distinguish between the various isomerides, the 
alcohols may be considered as derivatives of methyl alcohol 

f H 

I "FT 

or carbinol, CH 3 -OH or CJ H . Thus, propyl alcohol, 

[OH 

CH 3 -CH 2 .CH 2 -OH, may be termed ethyl-carbinol, because it 
may be considered as derived from carbinol by displacing one 
atom of hydrogen by the ethyl group C 2 H 5 -. Isopropyl 
alcohol, (CH 3 ) 2 CHOH, may be called dimethyl-carbinol, and 
regarded as derived from carbinol, by substituting two methyl 
or CH 3 - groups for two atoms of hydrogen. Such names as 
these serve to express the constitutions of the substances, as 
will be seen by considering the case of the four isomeric butyl 
alcohols, C 4 H 9 -OH, 



104 THE MONOHYDRIC ALCOHOLS. 

-CH 2 .CH 2 .CH a Normal butyl 

alcohol, or 

propyl carbinol 

(primary). 

^n 3 Isobutyl alcohol, 

pfi 3 >CH.CH 2 .OH, or cJ H or 

'** I TT isopropyl carbinol 

(primary). 

CH 3 - I C 2 H 5 Methylethyl carbinol 

,H-OH, or CX H (secondary). 




x^ OTJ . ,^.13 Trimethyl carbinol 

3 /C-UH, d ^ (tertiary). 

The alcohols are divided into three classes, namely, primary, 
secondary, and tertiary alcohols. 

Primary alcohols, as, for example, normal * propyl alcohol, 
CH 3 .CH 2 -CH 2 .OH, contain the group -CH 2 -OH, and may be 
considered as mono-substitution products of carbinol. On 
oxidation with chromic acid, &c., they are converted first into 
aldehydes (p. 118) and then into fatty acids (p. 145), the group 

s-TT 

-CH 2 -OH being transformed first into ~C\Q an( * then 

into -CX/i 

CH 3 -CH 2 .OH + = CHg-CHO + H 2 
CH 3 .CHO + = CH 3 .COOH. 

These oxidation products contain the same number of carbon 
atoms in the molecule as the alcohols from which they are 
obtained. 

Secondary alcohols, as, for example, isopropyl alcohol,! 
CH 3 -CH(OH).CH 3 , contain the group >CH-OH, and may be 

* The terra 'normal' is often applied to those primary alcohols which 
are derived from normal paraffins (p. 65). 

t The term ' iso ' is often applied to those primary or secondary alcohols 
which are derived from iso- or secondaiy paraffins (p. 65). 



THE MONOHYDRIC ALCOHOLS. 105 

regarded as di-substitution products of carbinol. On oxidation 

they are converted into ketones (p. 130) containing the same 

number of carbon atoms, the group >CH-OH becoming >CO, 

CH 3 .CH(OH).CH 3 + - CH 3 .CO-CH 3 + H 2 0. 

Tertiary alcohols, such as tertiary butyl alcohol, 
(CH 3 ) 3 C(OH), contain the group ^C-OH, and may be re- 
garded as tri-substitution products of carbinol. On oxida- 
tion they yield both ketones and fatty acids, which contain a 
smaller number of carbon atoms than the alcohol from which 
they are derived, the molecule of the latter being broken up. 
Tertiary butyl alcohol, or trim ethyl carbinol, (CH 3 ) 3 C(OH), 
for example, yields acetone, CH 3 -CO-CH 3 , acetic acid, 
CH 3 -CO-OH, carbon dioxide, and other products. It could 
not be converted by simple loss of hydrogen into a compound, 
(CH 3 ) 3 CO, containing the same number of carbon atoms 
a change which would be analogous to that undergone by 
primary and secondary alcohols because carbon is tetravalent 
and not pentavalent, as represented in this formula. 

Propyl alcohol (normal) or ethyl carbinol, CH 3 .CH 2 .CH 2 -OH, 
is one of the important constituents of fusel oil, from 
which it is prepared by fractional distillation. It is 
formed when propyl iodide is heated with freshly precipi- 
tated silver hydroxide and water, 

C 3 H 7 I + Ag-OH = C 3 H r OH + Agl. 

It is a colourless liquid of sp. gr. 0-804 at 20, boils at 97, 
and is miscible with water in all proportions. On oxidation 
with chromic acid, it is converted first into propaldehyde and 
then into propionic acid, 

CH 3 .CH 2 -CH 2 .OH + = CH 3 .CH 2 .CHO + H 2 

Propaldehyde. 

CH 3 .CH 2 .CH 2 .OH + 20 = CH 8 -CH 2 .CO.OH + H 2 0. 

Propionic Acid. 

Isopropyl alcohol, or dimethyl carbinol, (CH 3 ) 2 CH-OH, is 
best prepared by the reduction of acetone with sodium 
amalgam and water, 

CH 3 -CO-CH 3 + 2H = CH 8 -CH(OH).CH 



8 . 



106 THE MONOHYDRIC ALCOHOLS. 

It is a colourless liquid of sp. gr. 0-789 at 20, and boils at 
82, or about 16 lower than normal propyl alcohol. Oil 
oxidation it yields acetone, 

CH 3 .CH(OH).CH 3 + - CH 3 .CO-CH 3 + H 2 0, 
and when heated with zinc chloride it gives propylene, 
CH,.CH(OH).CH 8 = CH 3 -CH:CH 2 + H 2 0. 

There are four isomeric butyl alcohols, C 4 H 9 -OH. Normal 
butyl alcohol ', or propyl carbinol, CH 3 'CH 2 -CH 2 -CH 2 -OH, 
may be prepared by the reduction of butaldehyde, 
CH 3 'CH 2 -CH -CHO, and is produced during the fermenta- 
tion of glycerol by certain bacteria. It boils at 117. 

Isobutyl alcohol^ or isopropyl carbinol, (CH 3 ) 2 CH-CH 2 -OH, 
is contained in fusel oil. It boils at 107. 

Methylethyl carbinol, CH 3 -CH(OH)-C 2 H 5 , is obtained by 
reducing methyl ethyl ketone, CH 3 -CO-C 2 H 5 (p. 137), with 
sodium amalgam and water. It boils at 99 (740 mm.). 

Trimethyl carbinol, (CH 3 ) 3 C-OH, may be prepared by the 
action of zinc methyl, Zn(CH 3 ) 2 , on acetyl chloride, CH 3 -COC1, 
a reaction which is described below (p. 108). It may also be 
obtained from isobutyl alcohol, as explained later (p. 109). 
Trimethyl carbinol is one of the few alcohols which are 
solid at ordinary temperatures. It melts at 25, and boils 
at 83-84. 

Amyl alcohols, C 5 H n -OH. Of the eight structural 
isomerides theoretically capable of existing, the following 
two occur in fusel oil : 

Isobutyl carbinol, CH 3 v p p p 

(Isoamyl alcohol.) CH/ 'H 2 .UH 2 -UH. 

r^TT 

Active amyl alcohol. nTT ^ 3 >CH-CH 2 .OH. B.p. 129. 

L/xlg'Uxlg 

These alcohols form ordinary commercial amyl alcohol, and their 
boiling-points lie so close together that they cannot be separated by 
fractional distillation. A separation may, however, be accomplished 
by treating the mixture with sulphuric acid, and thus converting 
both alcohols into alkyl hydrogen sulphates, 

4 = C 5 H n .HS0 4 + H 2 O. 






THE MONOHYDRTC ALCOHOLS. 107 

By neutralising these compounds with barium hydrate, the barium 
salts, (C 5 H n -SO 4 ) 2 Ba, are obtained ; and, as the barium salt of iso- 
butyl carbinol is more sparingly soluble than that of active amyl 
alcohol, the two may be separated by fractional crystallisation. 
From the pure salts the respective alcohols are then obtained in 
a pure condition by distillation with dilute mineral acids, 

C 5 H n .HS0 4 + H 2 = C 5 H n -OH + H 2 S0 4 . 

Commercial amyl alcohol is prepared from fusel oil by frac- 
tionation, and is a mixture of about 87 per cent, of isobutyl 
carbinol and about 13 per cent, of active amyl alcohol. It has 
a pungent, unpleasant smell, boils at about 130, and is used as a 
solvent, and in the preparation of essences and perfumes (p. 193). 

SUMMARY AND EXTENSION. 

The Monohydric Alcohols. Hydroxy- derivatives of the 

paraffins of the general formula C n H 2n +rOH. 
The more important members of the series are the following. 

The letters p., s., t., in brackets, denote primary, secondary, and 

tertiary respectively. 

Name and Composition. B.p. Sp. gr. 

Methyl alcohol (p.) ............. CH 3 -OH, 66 0-812 at 

Ethyl alcohol (p.) ............... C 2 H 5 -OH, 78 0-806 .. 

Propyl alcohol (p.) ........... \PHOH 97 ' 817 " 

Isopropyl alcohol (s.) ........ j^s^rv 82 . 816 (( 

Butyl alcohol (p.) ............ >, 117 0-823 ,. 

Isobutyl alcohol (p.) ......... IP w nw 107 ' 816 



Methylethyl carbinol (s.).. f4, ggo Q 827 afc 2QO 

Tertiary butyl alcohol (t.)J 83- 0-786 ., 

Active amyl alcohol (p.)..."\ 129 " 

Isoamyl alcohol (p.) ......... L .-. 131 0-825 .. 

n- <i -i r ^Jtiii-uri, 
Six other isornerides of I 

little importance ......... ' 

Methods of Preparation. Methyl alcohol is prepared from the 
products of the dry distillation of wood. Ethyl alcohol is obtained 
by the alcoholic fermentation of sugars by means of yeast; the 
fusel oil produced at the same time contains propyl, isobutyl, 
active amyl, and isoamyl alcohols. 

The alcohols are formed when the halogen substitution products 
of the paraffins are heated with water, dilute aqueous alkalies, or 
moist freshly precipitated silver hydroxide, 

CH 3 Br + KOH = CH 3 -.OH + KBr C 3 H 7 I + Ag-OH = C 3 H r OH + Agl ; 



108 THE MONOHYDRIC ALCOHOLS. 

more readily by heating these halogen derivatives with silver or 
potassium acetate, and decomposing the products with potash, 
C 2 H 5 I + C 2 H 3 O 2 Ag = C 2 H 5 -C 2 H 3 2 + Agl 

Silver Acetate. Ethyl Acetate. 
C 2 H 5 .C 2 H 3 2 + KOH = C 2 H 5 -OH + C 2 H 3 2 K. 

This method gives very good results, and is much used in the 

preparation of the higher alcohols, because the halogen derivatives 

of the higher paraffins (such as hexyl chloride, C 6 H 13 C1), when 

treated directly with alkalies, are mainly converted into olefines, 

CH 3 .CH 2 .CH 2 -CH 2 .CHo-CH 2 Cl + KOH = 

CH 3 .CH 2 .CH 2 .CH 2 .CH:CH 2 + KC1 + H 2 0, 

so that the yield of alcohol is small. 

Alcohols are also formed when the hydrocarbons of the olefine 
series are dissolved in sulphuric acid, and the solutions boiled with 
water, 

C 3 H 6 + H 2 S0 4 = C 3 H 7 .HSO 4 
C 3 H 7 .HS0 4 + H 2 = C 3 H 7 -OH + H 2 S0 4 , 

and when aldehydes and ketones are reduced with nascent hydro- 
gen, aldehydes giving primary, ketones secondary, alcohols, 
CH 3 .CH 2 -CHO + 2H = CH 3 -CH 2 -CH 2 .OH 



i 



Tertiary alcohols are, as a rule, more difficult to obtain than the 
primary or secondary compounds ; they are usually prepared by 
gradually adding the chloride of a fatty acid to excess of a zinc 
alkyl derivative. Thus acetyl chloride, CH 3 -COC1, acts on zinc 
methyl, Zn(CH 3 ) 2 , forming a compound which, when treated with 
water, yields trimethyl carbinol, (CH 3 ) 3 C-OH. 

In this reaction the zinc methyl and acetyl chloride form a 
crystalline compound, 

^0 /0-Zn-CH 3 

CH 3 -C<; +Zn(CH 3 ) 2 =CH 3 -C^CH 3 

X C1 X C1 

which is then very slowly acted on by a further quantity of zinc 
methyl, 

/0-Zn.CH 3 /0-Zn-CH 3 

/~^TT f*i f^TT -U 7"iiff"^T-T ^ OTT C^~- Ol-T t /^TT 7-n C^\ 

3 \P1 3 323 \ 8 8 

\J\. v^Xlo 

This product is decomposed by water, when trimethyl carbinol, 
methane, and zinc hydroxide are obtained, 

X)-Zn.CH 3 /OH 

~ ~, +2H 2 O = CH 3 -C^CH 3 + Zn(OH) 2 + CH 4 . 

^CH 3 



THE MONOHYDRIC ALCOHOLS. 109 

Other tertiary alcohols may be prepared by employing other zinc 
alkyl compounds and other acid chlorides. 

Conversion of Primary into Secondary and Tertiary Alcohols. 
A secondary alcohol may be prepared from the corresponding 
primary compound by first converting the latter into an olefine by 
treating with dehydrating agents such as H 2 SO 4 , ZnCl 2 and P 2 5 , 

CH 3 .CH 2 .CH 2 .OH = CH 3 .CH :CH 2 + H 2 O. 

The olefine is then dissolved in fuming sulphuric acid, when an 
alkyl hydrogen sulphate is formed, the S0 4 H- group uniting with 
that carbon atom which is combined with the least number of 
hydrogen atoms, 

PTT 

CH 3 .CH :CH 2 + H 2 SO 4 = : 3 >CH -S0 4 H. 



The alkyl hydrogen sulphate is finally converted into a secondary 
alcohol by boiling with water, 



34 H + H 2 = *>CH.OH + H 2 S0 4 . 

In a similar manner, a primary alcohol, such as isobutyl alcohol, 
may be converted into the tertiary alcohol, trimethyl carbinol, 



SO 4 H ~* CH 3 OH 

Physical Properties. No gaseous alcohols are known. The 
members up to C^H^O are, with few exceptions, neutral, colourless 
liquids, possessing a characteristic odour and a burning taste. 
Trimethyl carbinol and all the higher alcohols, such as cetyl 
alcohol, C^Hgg-OH, which occurs in spermaceti in combination 
with palmitic acid, and melissyl alcohol, C 30 H 61 -OH, which is found 
in beeswax, also in combination with palmitic acid, are solids. 
Methyl, ethyl, and the propyl alcohols are miscible with water, 
but as the series is ascended the solubility in water rapidly 
decreases, the amyl alcohols, for example, being only sparingly 
soluble. The alcohols are miscible in all proportions with most 
organic liquids. The sp. gr. gradually increases, and the boiling- 
point rises on passing up the series ; the primary alcohols, however, 
boil at a higher temperature than the secondary, and the latter at 
a higher temperature than the tertiary isomerides, as shown in the 
table (p. 107) ; the regular variation in physical properties is, there- 
fore, obvious only when alcohols of similar constitution are com- 
pared. It may also be pointed out that, as a rule, the first member 
of a homologous series shows a somewhat abnormal behaviour ; 



110 THE MONOHYDRIC ALCOHOLS. 

for example, methyl alcohol has a higher sp. gr. than ethyl alcohol, 
and its boiling-point is only 12 lower than that of ethyl alcohol ; 
in the case of the higher homologues, the difference between the 
boiling-points of two consecutive normal alcohols is about 20. 

Chemical Properties. The fact that the alcohols interact with 
other compounds so much more readily than the paraffins is due to 
the presence of the hydroxyl- group, the rest of the molecule 
remaining unchanged, except under exceptional circumstances. 
In many reactions the alcohols behave as alkyl substitution pro- 
ducts of water ; in others, their similarity to metallic hydroxides 
is more marked. 

They dissolve sodium and potassium with evolution of hydrogen, 

2C 3 H 7 -OH + 2Na = 2C 3 H 7 ONa + H 2 . 

They interact with acids, forming esters or ethereal salts, such as 
CH 3 C1, C 2 H 5 Br, C 3 H 7 .HSO 4 , CH r COOC 2 H 5 . 

They are converted into halogen derivatives of the paraffins 
when treated with PC1 5 , PC1 3 , POC1 3 (compare foot-note p. 92), 
or with the corresponding bromo-derivatives, or with amorphous 
phosphorus and iodine, 

PC1 5 + C 3 H 7 -OH = C 3 H 7 C1 + POC1 3 + HC1. 

They are converted into olefines by dehydrating agents, such as 
H S0 4 or ZnCl 2 , 

CH 3 .CH 2 .OH = CH 2 :CH 2 + H 2 O. 

The action of oxidising agents varies with the nature of the 
alcohol. Primary alcohols are converted into aldehydes, and then 
into fatty acids, secondary alcohols into ketones, and in both cases 
the oxidation products contain the same number of carbon atoms in 
the molecule as the alcohol from which they are formed, 

CH 3 .CH 2 .CH 2 .OH + = CH 3 .CH 2 .CHO + H 2 
CH 3 .CH(OH)-CH 3 + O = CH 3 .CO.CH 3 + H 2 O. 

Tertiary alcohols do not yield oxidation products containing the 
same number of carbon atoms as the alcohol, but are decomposed, 
giving a mixture of simpler acids or of acid and ketone. The three 
classes of alcohols can therefore be distinguished by their different 
behaviour on oxidation. 



THE ETHERS. Ill 

CHAPTER VII. 

THE ETHERS. 

The ethers, such as methyl ether, CH 3 -0-CH 3 , methyl ethyl 
ether, CH 3 -0'C 2 H 5 , &c., are substances which contain two 
hydrocarbon groups, such as CH 3 -, C 2 H 5 -, and C 3 H 7 -, united 
by an oxygen atom. They are related to the metallic oxides 
in the same way as the alcohols to the metallic hydroxides. 
CH 3 -OH corresponds with K-OH 

CH 3 .o.CH 3 K.O-K. 

o o 

Methyl ether, CH 3 -OCH 3 , may be prepared by the action 
of sulphuric acid on methyl alcohol, 

2CH 8 .OH = CH 3 .0-CH 3 + H 2 O. 

It is a gas which liquefies at 23 (760 mm.), and dissolves 
readily in water (1 vol. of water dissolves 37 vols. of the 
ether at 18). 

Ethyl ether, ether, or sulphuric ether, C 2 H 5 -0-C 2 H 5 , is 
formed, together with sodium iodide, when sodium ethoxide 
is warmed with ethyl iodide (Williamson), 

C 2 H 6 -ONa + C 2 H 5 I --- C 2 H 5 -O.C 2 H 5 + Nal. 

It is also produced when ethyl alcohol is heated w T ith sulphuric 
acid under suitable conditions, 

2C 2 H 5 .OH _ C 2 H 5 .0-C 2 H 5 + H 2 0. 

Ethyl ether is prepared by the following method : 

A mixture of five parts of 90 per cent, alcohol and nine 
parts of concentrated sulphuric acid is heated in a flask fitted 
with a tap funnel and thermometer, and connected with a 
condenser (fig. 20). As soon as the temperature rises to 140 
the mixture begins to boil, and ether distils over. Alcohol is 
now slowly run in from the tap funnel, the temperature being 
kept at 140-145, and the process continued until a consider- 
able quantity of ether has collected. The crude product in the 



112 



THE ETHERS. 



receiver is a mixture of ether, alcohol, and water, and contains 
sulphur dioxide. It is shaken with dilute soda in a separat- 
ing funnel ; the layer of ether which collects on the surface is 
then separated, dried over calcium chloride or quicklime, and 
purified by redistillation from a water-bath. The ether still 
contains traces of water and alcohol, which may be got rid of 
by adding pieces of bright sodium, allowing to stand for some 




Fig. 20. 

hours, and again distilling. Sodium ethoxide and sodium 
hydroxide remain, and pure ether passes over. 

The formation of ether from alcohol takes place in two 
stages. When alcohol is heated with sulphuric acid, it is 
converted into ethyl hydrogen sulphate (p. 185), 

C 2 H 5 .OH + H 2 S0 4 = C 2 H 5 .HS0 4 + H 2 ; 
this compound then interacts with alcohol, yielding ether and 
sulphuric acid, 

C 2 H 5 -HS0 4 + C 2 H 5 .OH = C 2 H 5 .0-C 2 H 5 + H 2 S0 4 . 



THE ETHERS. 113 

This explanation of the formation of ether was first given 
by Williamson; that it is the true one is shown by the 
fact that ether is formed when pure ethyl hydrogen sulphate 
is heated with alcohol. 

Now, since the sulphuric acid necessary for the conversion 
of the alcohol into ethyl hydrogen sulphate is regenerated 
when the latter is heated with alcohol, a given quantity of 
the acid might, theoretically, convert an unlimited quantity 
of alcohol into ether. As a matter of fact, a small quantity 
of sulphuric acid can transform a very large quantity of 
alcohol into ether, but the process has a limit, because the 
acid becomes diluted by the water formed in the first stage of 
the reaction, and part of it is reduced by the alcohol, with 
formation of sulphur dioxide. Nevertheless, this method of 
preparing ether, by the continuous addition of alcohol to a 
solution of alcohol in sulphuric acid, is termed the continuous 
process* 

Ether is a colourless, mobile, neutral, pleasant-smelling 
liquid of sp. gr. 0-736 at 0. It boils at 35, and does not 
solidify at - 80. It is very volatile, and highly inflammable, 
its vapour forming an explosive mixture with air or oxygen, 

C 4 H 10 + 60 2 = 4C0 2 + 5H 2 0, 

so that all experiments in which ether is used should be 
conducted at least ten feet away from all flames or hot objects. 
Ether is soluble in about ten times its own volume of water, 
and is miscible with alcohol and other organic liquids in 
all proportions. 

Compared with alcohol, ether is a very inactive substance. 
It is not acted on by sodium or potassium, by alkalies or 
weak acids, or by phosphorus pentachloride in the cold. 

* If, instead of sulphuric acid, benzenesulphonic acid (Part II. p. 395) be 
used (Krafft), the process is really continuous, as this acid is not reduced by 
the alcohol and does not retain the water which is produced, but allows it 
to distil over with the ether, 

C 6 H 5 .SO 2 -OH + C 2 H 5 .OH = C 6 H 5 .S0 2 -OC 2 H 5 + H 2 O 
C 6 H 5 .SO 2 .OC 2 H 5 + C 2 H 5 -OH = C 2 H 5 .O.C 2 H 5 + C 6 H 5 -SO 2 -OH. 

Org. H 



114 THE ETHERS. 

Concentrated acids, however, decompose ether, with formation 
of esters or ethereal salts (p. 174), 

(C 2 H 5 ) 2 + 2H 2 S0 4 = 2C 2 H 5 -HS0 4 + H 2 
(C 2 H 5 ) 2 + 2HI = 2C 2 H 5 I + H 2 0. 

Ether is used in considerable quantities in surgery as 
an anaesthetic, since, like chloroform, it causes insensibility 
when inhaled ; it is also very largely employed as a solvent 
for resins, fats, oils, alkaloids, &c. 

Constitution of Ether. Since ether is produced by the 
action of ethyl iodide, C 2 H 5 I, on sodium ethoxide, C 2 H 5 -ONa, 
it may be concluded that it is formed by the substitution 
of the monovalent C 2 H 5 - group for the sodium atom, and its 
constitution may be expressed by the formula C 2 H 5 -0-C 2 H 5 . 
When represented by this formula, several facts concerning 
the behaviour of ether are brought to mind. Ether, unlike 
alcohol, contains no HO- group, and therefore it is not 
acted on by sodium or potassium, or by phosphorus penta- 
chloride ; and, not being a hydroxide, it does not interact 
with acids to form a salt and water. Ether was formerly 
regarded as an anhydride of alcohol and as being formed 
from alcohol (2 mols.) by the removal of the elements of 
water, just in the same way as nitric anhydride is formed 
from nitric acid, 

2C 2 H 5 .OH = (C 2 H 5 ) 2 + H 2 2N0 2 -OH = (N0 2 ) 2 + H 2 0. 

It is better compared with the metallic oxides, and regarded as 
ethyl oxide, since it is related to alcohol or ethyl hydroxide 
in the same way as the metallic oxides to the metallic 
hydroxides, 

C 2 H 5 -OH C 2 H 5 .0-C 2 H 5 or (C.H^O 

K-OH K-O-K . or K 2 0. 

Finally, it may be regarded as a di-substitution product of 
water, the mono-substitution product being the corresponding 
alcohol, 

H.OH C 2 H 5 .O.H C 2 H 5 -O.C 2 H 5 . 



THE ETHERS. 115 

The Tiomologues of ether are very similar to ethyl ether in 
properties. 

SUMMARY AND EXTENSION. 

Some of the more important higher ethers are the following : 
Dipropyl ether (CH 3 .CH 2 .CH 2 ) 2 ............................. B.p. 90-7 

Di-isopropyl ether ( 3 >CH) 2 ........................... 69 

Di-isobutyl ether ( 3 >CH.CH 2 ) 2 O ....................... 122 

Di-isoamyl ether (C 5 H n ) 2 O ...................................... n 173 

General Methods of Formation. The ethers may he ohtained 
by treating the sodium compounds of the alcohols with the alkyl 
halogen compounds, 



but they are usually prepared by heating the alcohols with 
sulphuric acid. If a mixture of two alcohols be treated with 
sulphuric acid, three ethers are formed. A mixture of methyl and 
ethyl alcohols, for example, yields methyl ether, ethyl ether, and 
methyl ethyl ether, CH 3 -O-C 2 H 5 . The formation of the two first- 
named compounds will be understood from the equations given 
above in the case of ethyl ether. Methyl ethyl ether is produced 
by the interaction (a) of methyl hydrogen sulphate and ethyl 
alcohol, (b) of ethyl hydrogen sulphate and methyl alcohol, 

CH 3 .HSO 4 + C 2 H 5 -OH - CH 3 .O.C 2 H g + H 2 SO 4 
C 2 H 5 -HS0 4 + CH 3 .OH = C 2 H 5 .0 .CH 3 + H 2 S0 4 . 

All ethers, such as methyl ethyl ether, CH 3 'O-C 2 H 5 , which contain 
two different hydrocarbon groups are termed mixed ethers, to distin- 
guish them from simple ethers, such as ethyl ether, C 2 H 5 -O-C 2 H 5 , 
and those given in the above table, which contain two identical 
groups. Mixed ethers can also be obtained by treating the sodium 
compounds of the alcohols with alkyl halogen compounds, 

CH 3 .ONa + C 3 H 7 I = CH 3 .0-C 3 H 7 + Nal. 

General Properties. With the exception of methyl ether, which 
is a gas, the ethers are mobile, volatile, inflammable liquids, 
specifically lighter than water ; they all boil at much lower tem- 
peratures than the corresponding alcohols. In chemical proper- 
ties they closely resemble ethyl ether. They are not acted on by 
alkalies or alkali metals, and do not interact with dilute acids ; 
but they are decomposed when heated with strong acids, yielding 
ethereal salts, 



116 THE ETHERS. 

(C 2 H 5 ). 2 O + 2H 2 S0 4 = 2C 2 H 5 .HS0 4 + H 2 O 
CH 3 -O -C 2 H 5 + 2HBi CH 3 Br + C 2 H 5 Br + H 2 0. 

Chlorine and bromine act on ethers, forming substitution products 
such as 

CH 2 C1.0.CH 3 , CH 2 Br.O-CH 2 Br, C 2 H 5 .O-C 2 H 4 C1, &c. 

The ethers exist in isomeric forms. There are, for example, three 
compounds of the formula C 4 H 10 0, 

CH 3 .O.CH 2 .CH 2 .CH 3 CH 3 .O.CH< 3 CH 3 .CH 2 .O.CH 2 .CH 3 . 

ui 3 

Methyl Propyl Ether. Methyl Isopropyl Ether. Ethyl Ether. 

These three ethers are also isomeric with the four butyl alcohols 
C 4 H 9 -OH (p. 104). 

RADICLES. 

On studying the equations which represent the interactions 
of organic compounds, the fact that certain groups of atoms 
often remain unchanged during a whole series of operations is 
particularly noticeable. Ethyl chloride, for example, may be 
converted into ethyl alcohol, the latter may be transformed 
into ethyl iodide, and this again may be converted into 
butane, but during all these interactions the group C 2 H 5 - 
remains unchanged, and behaves, in fact, as if it were a 
single atom, 

C 2 H 5 -C1 + H-OH = C 2 H 5 .OH + HC1 
C 2 H 5 -OH + HI = C 2 H 5 -I + H 2 
2C 2 H 5 .I + 2Na - C 2 H 5 .C 2 H 5 + 2tfal. 

Numerous examples of a similar kind might be quoted; 
amongst others, the changes by which the five compounds, 
CH 3 .C1, CH 3 .OH, CH 3 .0-CH 3 , CH 8 J, and CH 3 .CH 3 , may 
be successively transformed one into the other. 

Groups of atoms, such as C 2 H 5 - and CH 3 -, which act 
like single atoms, and which enter unchanged into a number 
of compounds, are termed radicles, or sometimes compound 
radicles. 

Kadicles may be monovalent, divalent, &c., according as 
they act like monad, dyad, &c., atoms ; the radicles C 2 H 5 - 
and CH 3 -, for example, are monad radicles, because they 



RADICLES. 117 

combine with one atom of hydrogen or its valency equivalent, 
as shown in the above equations. 

The name alkyl or alcohol radicle is given to all the mono- 
valent groups of atoms which are, theoretically, obtained on 
taking away one atom of hydrogen from the paraffins, methane, 
ethane, propane, butane, &c. ; the distinctive names of these 
radicles are derived from those of the hydrocarbons by 
changing ane into yl, thus : methyl, CH 3 - ; ethyl, C 2 H 5 - or 
CH 3 -CH 2 -; propyl, C 3 H r - or CH 3 -CH 2 -CH 2 - ; isopropyl, 
C 3 H 7 - or (CH 3 ) CH-; butyl, C 4 H 9 - or CH 3 .CH 2 -CH 2 .CH 2 -; 
isobutyl, C 4 H 9 - or (CH 3 ) 2 CH.CH 2 - &c. 

The compounds formed by the combination of these hypo- 
thetical alkyl radicles with hydrogen, as, for example, CH 3 -H, 
C 2 H 5 -H, C 3 H 7 -H, are sometimes called the alkyl hydrides, 
and are identical with the paraffins ; the corresponding 
chlorine compounds, such as CH 3 -C1, C 2 H 5 -C1, C 3 H 7 -C1, are 
termed the alkyl chlorides, and so on. The letter R is 
frequently employed to represent any alkyl radicle, as, for 
example, in the formulae R-OH (alcohols) and R-O-R (simple 
ethers). The symbols Me, Et, Pr, Bu, &c. are also often used 
instead of CH 3 -, C 2 H 5 -, CgH^-, C 4 H 9 -, &c., and when the 
radicle may assume isomeric forms, as, for example, in the 
case of C 3 H r -, which may be either CH 3 'CH 2 -CH 2 - or 
(CH 3 ) 2 CH-, the former is represented by Pr*, the latter by 
Pr 3 . 

The name alkylene is given to the divalent radicles, which 
(except methylene) may be actually obtained by taking away 
two atoms of hydrogen from the paraffins. The alkylenes are 
methylene, CH 2 = ; ethylene, C 2 H 4 = ; propylene, C 3 H 6 = ; buty- 
lene, C 4 H 8 =, &c. ; and the compounds which they form, with 
chlorine, for example, such as CH 2 :C1 2 , C 2 H 4 :C1 2 , are termed 
collectively the alkylene chlorides, &c. 

Trivalent hydrocarbon radicles, such as glyceryl, C 3 H 5 = 
(p. 257), are seldom met with. 

Other radicles of great importance are.: hydroxyl, -OH; 
carbonyl, =CO ; carboxyl, -CO-OH ; cyanogen, -CN ; acetyl, 



118 ALDEHYDES AND KETONES. 

-CO-CH 3 , and the aldehyde, -CHO, amido, -NH 2 , and 
nitro, -N0 2 groups. 

One of the principal objects ivhich the student should keep 
in view is, to obtain a clear idea of the behaviour of these 
and of other groups, and to learn how they determine the 
properties of the substances containing them. 



CHAPTER VIII. 

ALDEHYDES AND KETONES. 

The aldehydes form a homologous series of the general 
formula C n H 2n O, or C M H 2n+1 -CHO ; they are derived from 
the primary alcohols C w H 2w+1 -CH 2 -OH by the removal of 
two atoms of hydrogen from the -CH 2 -OH group, 

Paraffins. Alcohols. Aldehydes. 

H-CH 3 H-CH 2 -OH H-CHO 

CH 3 .CH 3 CH 3 .CH 2 .OH CH 3 .CHO 

C 2 H 5 .CH 3 C 2 H 5 .CH 2 -OH C 2 H 5 .CHO 

The word aldehyde is a contraction of aZcohol de/w/drogenatum, 
this name having been originally given to acetaldehyde, 
because it is formed when hydrogen is taken from alcohol 
by a process of oxidation. 

Formaldehyde, or methaldehyde, H-CHO, is said to occur 
in those plant cells which contain the green colouring 
matter chlorophyll, and is possibly an intermediate product 
in that wonderful process the formation of starch and sugars 
from the carbon dioxide which the plant absorbs from the air. 

Formaldehyde is produced when carbon dioxide is reduced, 
in aqueous solution, with palladium hydride,* and it is also 
formed in small quantities when calcium formate is subjected 
to dry distillation, 

(H.COO) 2 Ca = H-CHO + CaC0 3 . 

* The substance obtained when hydrogen is passed over warm palladium. 



ALDEHYDES AND KETONES. 119 

It is prepared by passing a stream of air, saturated with 
the vapour of methyl alcohol, through a tube containing a 
copper spiral, or platinised asbestos, heated to dull redness;* 
the change is a process of oxidation, 

CH 3 -OH + = H-CHO + H 2 0. 

The pungent-smelling aqueous solution which collects in the 
receiver may contain, under favourable conditions, as much 
as 30-40 per cent, of formaldehyde, together with methyl 
alcohol. On evaporating the solution on a water-bath or 
even at ordinary temperatures, the formaldehyde gradually 
undergoes change, and is converted into parafornialdehyde 
(p. 120), which remains as a white solid. 

The formation of formaldehyde may be readily demon- 
strated by heating a spiral of platinum wire to dull redness 
and quickly suspending it over methyl alcohol contained in 
a beaker; the spiral begins to glow, and irritating vapours 
are rapidly evolved, a slight but harmless explosion usually 
taking place. 

Formaldehyde is a gas at ordinary temperatures, but when 
cooled it condenses to a liquid, boiling at -21. Even at 
this low temperature it slowly changes into trioxymetliylene 
(p. 121), and at ordinary temperatures it does so with great 
rapidity, the process involving a considerable development 
of heat. Aqueous solutions of formaldehyde have a very 
penetrating, suffocating odour and a neutral reaction; they 
have also a powerful reducing action, since formaldehyde 
readily undergoes oxidation, yielding formic acid, 

H.CHO + O=H.COOH. 

When its aqueous solution is mixed with an ammoniacal 
solution of silver hydroxide a silver mirror is obtained, 

H-CHO + Ag 2 = H-COOH + 2Ag ; 

mercuric chloride is also reduced, first to mercurous chloride, 
then to mercury. 

Formaldehyde is a strong antiseptic agent, and is fatal to 

* Unless special precautions be taken, explosions frequently occur. 



120 ALDEHYDES AND KETONES. 

bacteria of various kinds; an aqueous solution containing 
about 40 per cent, of formaldehyde (or of its hydrates) is sold 
under the name of formalin, and is an important article of 
commerce, being used as an antiseptic, disinfectant, and 
preservative, and as a reducing agent. 

When a concentrated aqueous solution of formaldehyde is mixed 
with a saturated solution of sodium hydrogen sulphite, direct com- 
bination takes place, a compound of the constitution OH-CH 2 -S0 3 Na 
being formed. Formaldehyde interacts with hydroxylamine in 
aqueous solution, yielding formaldoxime, 



a substance which is only known in solution since it very readily 
undergoes polymerisation. 

Constitution. Since carbon is tetravalent, there is only 
one way of expressing graphically the constitution of formal- 

/TT 
dehyde, CH 2 0, namely, by the formula H-C. In the 



formation of formaldehyde by the oxidation of methyl 
alcohol, CH 3 -0-H, one of the hydrogen atoms of the CH 3 - 
group is probably oxidised to -OH, thus giving an unstable 
compound, CH 2 (OH) 2 , which, unless kept in solution, decom- 
poses into CH 2 and H 2 0. It will be seen that the oxygen 
atom in formaldehyde is represented as being in a state of 
combination different from that existing in methyl alcohol 
namely, as joined to carbon by two lines instead of one. 
Formaldehyde is, in fact, an nnsaturated compound, and is 
capable of forming additive products under certain condi- 
tions; it must be carefully noted, however, that the atoms 
or groups with which formaldehyde unites directly are not, 
generally speaking, those which combine most readily with 
two unsaturated carbon atoms ; a double binding between 
carbon and oxygen must be distinguished from a double 
binding between two carbon atoms although in both cases 
it indicates the power of forming additive products. 

Paraformaldehyde is formed, as stated above, when an 
aqueous solution of formaldehyde is evaporated ; it is a colour- 



ALDEHYDES AND KETONES. 121 

less amorphous substance, soluble in warm water, and has 
probably the molecular formula (CH 2 0) 2 . 

Trioxymethylene, or metaformaldehyde, (CH 2 0) 3 , is formed 
by the polymerisation of anhydrous liquid formaldehyde (p. 1 1 9), 
and also when paraformaldehyde is carefully heated ; it is an 
indefinitely crystalline compound which sublimes readily, and 
melts at 171. When strongly heated it is completely de- 
composed into pure, gaseous formaldehyde, CH 2 0, as is proved 
by vapour density determinations; but as the gas cools, 
trioxymethylone is again produced. When heated with a 
large quantity of water at about 140, it is also converted 
into formaldehyde. 

Polymerisation. It will be seen from what has already been 
stated, that formaldehyde readily changes, either spontaneously 
or when heated, giving new compounds, which can be recon- 
verted into formaldehyde, CH 2 0, by simple means. As the 
new compounds have the same percentage composition as the 
parent substance, their molecules may be regarded as having 
been produced by the aggregation of several molecules of 
the latter. This view led to the introduction of the word 
polymerisation, which means the change of some (simple) 
substance into another of the same percentage composition, 
but having a molecular weight equal to several multiples of 
that of the parent substance j the more complex compounds 
thus formed were then termed polymers, polymerides, 01 
polymeric modifications of the original substance, and they 
received names, such as paraformaldehyde and metaformalde- 
hyde, merely in order to express their origin or derivation. The 
relation between formaldehyde and its polymeric modifications 
was thus regarded as being somewhat similar to that exist- 
ing between the several allotropic forms of an element. At 
the present time it is recognised that a polymeric modification 
may show no relation or similarity to the parent substance 
whatsoever ; that its molecules are not merely aggregates or 
collections of simpler molecules, but are formed by two or 
more molecules of the latter uniting together chemically to 



122 ALDEHYDES AND KETONES. 

form a new and distinct compound, which in many cases 
cannot be reconverted into the original substance. 

Polymerisation is, then, merely an ordinary chemical 
change, resulting in the formation of a new compound, 
whose molecular weight is a multiple of that of the 
original substance because it is produced from the latter 
without loss or gain in weight ; other examples of this 
change are given later (pp. 126, 128). 

Formaldehyde forms several polymeric modifications, and the 
readiness with which it undergoes polymerisation is one of 
its most characteristic properties.- When its aqueous solution 
is treated with lime-water or other weak alkali, formaldehyde 
undergoes polymerisation into formose, a mixture of sub- 
stances, some of which have the composition (CH 2 0) 6 or 
C 6 H 12 6 , and belong to the sugar group. This reaction is 
of great interest, since it shows that complex vegetable sub- 
stances such as the sugars may be formed by very simple 
means (p. 272). 

Methylal, CH 2 (OCH 3 ) 2 , is an important derivative of 
formaldehyde. It may be obtained by boiling aqueous 
formaldehyde with methyl alcohol and a small quantity 
of sulphuric acid, but is usually prepared by oxidising 
methyl alcohol with manganese dioxide and sulphuric acid, 
the formaldehyde first produced combining with the un- 
changed methyl alcohol, 

H-CHO + 2CH 3 .OH = H-CH(OCH 3 ) 2 + H 2 0. 

Methylal, a pleasant-smelling liquid, which boils at 42 and 
is readily soluble in water, is used in medicine as a soporific. 
When distilled with dilute sulphuric acid, it gives an aqueous 
solution of methyl alcohol and formaldehyde, a reaction which 
may be conveniently employed for preparing the latter. 

Acetaldehyde, or ethaldehyde, CH 3 -CHO, is contained in 
the 'first runnings' obtained in the rectification of refined 
spirit (p. 101), having been formed by the oxidation of the 
alcohol during the process of filtration through charcoal; 



ALDEHYDES AND KETONES. 123 

it is formed when a mixture of calcium acetate and calcium 
formate is submitted to dry distillation, 

(CH 8 .COO) 2 Ca + (H.COO) 2 Ca = 2CH 3 -CHO + 2CaC0 3 , 
and is prepared by oxidising alcohol with potassium di- 
chromate and sulphuric acid, 

CH 3 .CH 2 .OH + = CH 3 .CHO + H 2 0. 

Coarsely powdered potassium dichromate (3 parts) and water 
(12 parts) are placed in a capacious flask fitted with a tap-funnel 
and attached to a condenser, and a mixture of alcohol (3 parts) and 
concentrated sulphuric acid (4 parts) is then added drop by drop, 
the flask being gently heated on a water-bath, and shaken almost 
constantly, during the operation. A vigorous action sets in, and 
a liquid, which consists of aldehyde, alcohol, water, and small 
quantities of acetal (see below), collects in the receiver. This 
liquid is now fractionally distilled from a water-bath, the tempera- 
ture of which is not allowed to rise above 50, when the aldehyde, 
being very volatile, passes over, most of the impurities remaining 
in the flask ; the distillate is then mixed with dry ether, and the 
mixture saturated Avith dry ammonia, when a crystalline precipitate 
of aldehyde ammonia (see below) is obtained. This substance is 
transferred to a filter, washed with ether, and then decomposed by 
distillation with dilute sulphuric acid at as low a temperature 
as possible ; the aldehyde is finally dehydrated by distillation with 
coarsely powdered anhydrous calcium chloride, the receiver being 
well cooled with ice in this and in the previous operations. 

Acetaldehyde, or aldehyde, as it is usually called, is 
a colourless, mobile, very volatile liquid of sp. gr. 0-801 
at 0; it boils at 20-8. . It has a peculiar penetrating 
and suffocating odour, somewhat like that of sulphur 
dioxide, and when inhaled it produces cramp in the throat, 
and for some seconds takes away the power of respiration ; 
it is very inflammable, and mixes with water, alcohol, and 
ether in all proportions. Aldehyde is slowly oxidised to 
acetic acid on exposure to the air, and, like formaldehyde, it 
has powerful reducing properties ; it precipitates silver, in 
the form of a mirror, from ammoniacal solutions of silver 
hydroxide, being itself oxidised to acetic acid, 

CH 3 .CHO + Ag 2 = CH 3 .COOH + 2Ag. 



124 ALDEHYDES AND KETONES. 

When reduced with sodium amalgam and water, it is con- 
verted into alcohol, 

CHg-CHO + 2H = CH 3 .CH 2 .OH. 

Aldehyde interacts readily with hydroxylamine in aqueous 
solution, yielding a crystalline compound, acetaldoxime, 

CHg-CHO + NH 2 -OH = CH 3 .CH:NOH + H 2 0. 

When aldehyde is shaken with a concentrated solution of 
sodium hydrogen sulphite (sodium bisulphite) direct com- 
bination occurs, and a colourless substance of the com- 
position CH 3 -CHO,NaHS0 3 separates in crystals. This 
compound is readily decomposed by acids, alkalies, and 
alkali carbonates, aldehyde being liberated. Aldehyde also 
combines directly with dry ammonia, yielding a colourless, 
crystalline substance, aldehyde ammonia, CH 3 -CHO,NH 3 , 

QTT 

or CH 3 -CH ^^TTT 5 which is decomposed by acids, aldehyde 
JN Jtifj 

being regenerated. 

Aldehyde very readily undergoes polymerisation on treat- 
ment with acids, dehydrating agents, and other substances 
(see below). Its behaviour with alkalies is very characteristic ; 
when it is warmed with potash or soda a violent action sets 
in, and the aldehyde is converted into a brown substance 
called aldehyde resin. 

Aldehyde may be detected by its highly characteristic smell, 
by its reducing action on silver oxide, and by the ' magenta ' 
or ' rosaniline test ' (SchifF s reaction), which is carried out as 
follows : Sulphurous acid is added to a very dilute solution 
of rosaniline hydrochloride until the pink colour is just 
discharged; the solution to be tested is now added, when, 
if it contain a trace of aldehyde, a violet or pink colour 
immediately appears. This behaviour is not characteristic of 
acetaldehyde, as, with very few exceptions, all aldehydes give 
this reaction. 

Constitution. Aldehyde is formed by the oxidation of 
ethyl alcohol, just as formaldehyde is produced by the 



ALDEHYDES AND KETONES. 125 

oxidation of methyl alcohol, the final result being that two 
atoms of hydrogen are removed in both cases. Now, since 
methane and ethane are not oxidised by potassium dichromate 
and sulphuric acid, it may be assumed that the reason why 
these alcohols are so readily attacked is, because the presence 
of the hydroxyl-group affects the behaviour of the hydrogen 
atoms; if this be so, it seems probable that in the case of 
ethyl alcohol, as in that of methyl alcohol, two hydrogen 
atoms of the -CH 2 -OH are taken away, 



CH 3 .CH 2 .OH + = CH 3 .CH< = CH 3 -C + H 2 0, 



the hydrogen atoms of the CH 3 - group remaining undis- 
turbed because they are further removed from the influence 
of the hydroxyl-group. Judging from analogy, then, the 
constitution of aldehyde is expressed by the formula 

this view accords very well with the whole 

chemical behaviour of the compound, which is similar to 
that of formaldehyde. Aldehyde, unlike alcohol, does not 
contain a hydrogen atom displaceable by sodium or potas- 
sium, and does not form salts with acids; these facts are 
expressed by the above formula, which shows that aldehyde 
does not contain the HO- group. When aldehyde is 
treated with phosphorus pentachloride, one atom of oxygen 
is displaced by two atoms of chlorine (giving ethylidene 
chloride), a change which is very different from that 
which occurs when alcohol is acted on, and which affords 
further evidence that aldehyde is not a hydroxy-compound. 
This point is rendered very clear if the behaviour of alde- 
hyde and alcohol respectively with phosphorus pentachloride 
be represented side by side, 

CH 3 .CHO + PC1 6 = CH 3 .CHC1 2 + POC1 3 

CH 3 .CH 2 .OH + PC1 5 = CH 3 .CH 2 C1 + POC1 3 + HC1. 

The ftict that aldehyde has the power of combining directly 

with nascent hydrogen, ammonia, sodium hydrogen sulphite, 



126 ALDEHYDES AND KETONES. 

alcohol (see below), &c., is also indicated by the above 
constitutional formula. Acetaldehyde, like formaldehyde, is 
an unsaturated compound, and combines directly with two 
monad atoms or groups, as in its reduction to ethyl alcohol, 
in its conversion into aldehyde ammonia, &c. 

It must be concluded, therefore, that both formaldehyde 



and acetaldehyde contain the monovalent group -C/y which 

is usually written -CHO (not COH, which might be con- 
fused with C - OH) ; it is the presence of this aldehyde 
group which determines their characteristic properties, 
because nearly all the changes which these two alde- 
hydes undergo are limited to the group -CHO which 
they both contain; all aldehydes contain a group of this 
kind. 

Polymerisation of Acetaldehyde. Three well-defined 
poly me rides of aldehyde are known namely, aldol, par- 
aldehyde, and metaldehyde. 

Aldol, (C 2 H 4 0) 2 , or CH 3 .CH(OH>CH 2 .CHO, is produced 
by the action of dilute hydrochloric acid, or of zinc chloride, 
on aldehyde at ordinary temperatures. It is a colourless, 
inodorous liquid, miscible with water, and shows all the 
ordinary properties of an aldehyde. It can be distilled under 
reduced pressure without decomposing, but when distilled 
under ordinary pressure, or when heated with dehydrating 
agents, it is converted into crotonaldeJiyde (p. 263) and water, 

CH 3 -CH(OH) -CH 2 .CHO = CH 3 .CH: CH-CHO + H 2 0. 

Paraldehyde, (C 2 H 4 0) 3 , is readily produced by adding 
a drop of concentrated sulphuric acid to aldehyde at 
ordinary temperatures, an almost explosive action taking 
place. It is a colourless, pleasant-smelling liquid, boils 
at 124, and solidifies in the cold. It is soluble in water, 
its cold saturated solution becoming turbid on warming, 
as it is less soluble in hot than in cold water; whei 
distilled with a few drops of concentrated sulphuric acic 



ALDEHYDES AND KETONES. 127 

it is converted into aldehyde. Paraldehyde is used in 
medicine as a soporific. 

Metaldehyde, (C 2 H 4 0) 3 , is produced by the action of acids 
on aldehyde at low temperatures. It crystallises in colourless 
needles, and is insoluble in water ; it can be sublimed with- 
out decomposing, but on prolonged heating, it is converted 
into aldehyde, a change which is also readily brought about 
by distilling it with dilute sulphuric acid. 

Paraldehyde and metaldehyde show none of the ordinary 
properties of aldehydes, and do not contain the aldehyde or 
-CHO group ; in other words, they are not true aldehydes 
(p. 144). Metaldehyde is isomeric with paraldehyde, but its 
relation to the latter is not known exactly. 

Derivatives of Aldehyde. Acetal, CH 3 .CH(OC 2 H 5 ) 2 , is 
produced when a mixture of aldehyde and alcohol is heated 
it 100, or when alcohol is oxidised with manganese dioxide 
md sulphuric acid (compare methylal, p. 122), 

CH 3 .CHO + 2C 2 H 5 .OH = CH 3 .CH(OC 2 H 5 ) 2 + H 2 0. 

It is a colourless liquid, possessing an agreeable smell, and 
)iling at 104; when distilled with dilute acids it is decom- 
id into alcohol and aldehyde, 

CH 3 .CH(OC 2 H 5 ) 2 + H 2 = CH 3 .CHO + 2C 2 H 5 -OH. 

Chloral, or trichloraldehyde, CC1 3 -CHO, can be obtained 
the direct action of chlorine on aldehyde ; it was dis- 
)vered by Liebig while investigating the action of chlorine 
alcohol, and is manufactured on a large scale by saturating 
alcohol with chlorine, first at ordinary temperatures, and then 
at the boiling-point, the operation taking some days. The 
rstalline product, which consists for the greater part of 

OP TT 

loral alcolwlate, CC1 3 -CH<^ 2 5 , is distilled with con- 

mtrated sulphuric acid, and the oily distillate of crude 
chloral converted into chloral hydrate (see below). After 
)urifying the hydrate by recrystallisation from water, it is 
listilled with sulphuric acid, when pure chloral passes over. 



128 ALDEHYDES AND KETONES. 

The formation of chloral alcoholate by the action of chlorine 
on alcohol involves a long series of reactions, which it is unneces- 
sary to describe in detail because they are not sufficiently typical ; 
it may be noted, however, that the chlorine acts here both as 
an oxidising and as a chlorinating agent. 

Chloral is an oily liquid of sp. gr. 1-512 at 20, and boils 
at 97. It has a penetrating and irritating smell, and in 
chemical properties closely resembles aldehyde, a fact which 
was only to be expected, since it is a simple substitution 
product of aldehyde, and contains the characteristic aldehyde 
group. It has reducing properties, combines directly with 
ammonia, sodium hydrogen sulphite, &c., and on oxidation 
it is converted into trichloracetic acid (p. 166), just as alde- 
hyde is converted into acetic acid, 

CC1 3 -CHO + = CC1 3 .COOH. 

On the addition of small quantities of acids it very readily 
undergoes polymerisation, being transformed into a white 
amorphous modification called metachloral ; the same change 
takes place when chloral is kept for a considerable time. 
One of the most interesting reactions of chloral is its 
behaviour with boiling potash, by which it is quickly 
decomposed, giving chloroform (p. 175) and potassium 
formate, 

CC1 3 .CHO + KOH = CHC1 3 + H-COOK. 

Pure chloroform is often prepared in this way. 

Chloral Hydrate, CC1 3 .CH(OH) 2 . When chloral is poured 
into water it sinks as an oil at first, but in a few seconds the 
oil changes to a mass of colourless crystals of chloral hydrate, 
a considerable rise in temperature taking place. Chloral 
hydrate melts at 57, is readily soluble in water, and is 
decomposed on distillation with sulphuric acid, chloral 
passing over. In some respects it is a very stable substance ; 
it does not polymerise, and does not give the rosaniline 
reaction of aldehydes. These facts point to the conclusion 
that chloral hydrate does not contain the aldehyde group, 



ALDEHYDES AND KETONES. 129 

but that by combination with water the chloral has been con- 

OTT 

verted into a substance of the constitution CCl 3 -CH< n .* 

Chloral hydrate is extensively used in medicine as a 
soporific. 

Butyl-chloral, CH 3 .CHC1.CC1 2 -CHO, is formed when 
chlorine is passed into aldehyde, first in the cold and then 
at 100; it boils at 164-165 and combines readily with water, 
forming butyl-chloral hydrate, CH 3 .CHC1-CC1 2 -CH(OH) 2 , a 
crystalline substance melting at 78, which is used in 
medicine. 

The formation of butyl-chloral may be explained by assuming 
that chloracetaldehyde, produced by substitution, interacts with 
unchanged aldehyde, giving chlorocrotonaldehyde, 

CH 3 -CHO + CH 2 C1-CHO = CH 3 .CH:CC1.CHO + H 2 0, 
rhich then unites directly with chlorine (compare aldol, p. 126). 

Homologues of Acetaldehyde. The higher members of 
the homologous series of aldehydes, such as propaldehyde, 
2 H 5 -CHO, and butaldehyde, C 3 H^-CHO, may be produced by 
oxidation of the corresponding primary alcohols, or by 
te dry distillation of the calcium salts of the corresponding 
itty acids with calcium formate ; they resemble acetaldehyde 
chemical properties. 
Heptaldehyde, or CEnanthol, C 6 H 13 -CHO, is of consider- 
able interest because it is one of the products of the dry 
distillation of castor-oil. It is a colourless oil, boils at 154, 
and has a penetrating, disagreeable odour ; on oxidation it 
yields normal heptylic acid, C 6 H 13 -COOH (p. 160), and on 
reduction, normal heptyl alcohol, C 6 H 13 -CH 2 -OH. 

* Very few compounds containing two hydroxyl - groups united to the 
same carbon atom are known ; as a rule such compounds are very unstable 
and readily lose the elements of water, the group >C(OH) 2 giving 
>CO + F 2 (pp. 120, 125). 



Oi* 



130 ALDEHYDES AND KETONES. 

KETONES. 

The ketones, of which the simplest, acetone, CH 3 -CO-CH 3 , 
may be taken as an example, are derived from the secondary 
alcohols, such as isopropyl alcohol, CH 3 'CH(OH)-CH 3 , by 
the removal of two atoms of hydrogen from the -CH(OH) 
group, the process being, in fact, strictly analogous to the 
formation of aldehydes from the primary alcohols. Ketones 
are characterised by containing the divalent group ^>C = 
united with two alkyl radicles, as in CH 3 -CO-C 2 H 5 , 
C 2 H 5 ^CO-C 2 H 5 , and their composition may be expressed by 
the general formula C n H 2n O ; they are isomeric with the 
aldehydes containing the same number of carbon atoms. 

Propaldehyde, CH 3 .CH 2 .CHO 

Dimethyl ketone, CH 3 .CO-CH 3 
Butaldehyde, CH 3 .CH 2 .CH 2 .CHO 1 

Ethylmethyl ketone, CH 3 .CH 2 .CO-CH 3 J 4 H 8- 

Acetone, or dimethyl ketone, CH 3 -CO-CH 3 , occurs in 
small quantities in normal urine, and in cases of diabetes 
mellitus and acetonuria the quantity increases considerably. 
It also occurs in small quantities in the blood. 

Acetone is formed when isopropyl alcohol is oxidised with 
potassium dichromate and sulphuric acid, 



and is produced in considerable quantities during the dry 
distillation of wood and many other organic compounds, such 
as sugar, gum, &c. Crude wood-spirit, which has been freed 
from acetic acid (p. 90), consists in the main of a mixture of 
water, methyl alcohol, and acetone. The last two substances 
may be roughly separated by the addition of calcium chloride, 
which combines with the methyl alcohol ; the crude acetone 
may then be purified by distillation and by conversion into 
the bisulphite compound (see below). 

Acetone is prepared in the laboratory and on the large scale 
by the dry distillation of crude calcium (or barium) acetate, 



ALDEHYDES AND KETONES. 131 

(CH 3 .COO) 2 Ca = CH 3 .CO-CH 3 + CaC0 3 . 

The distillate is fractionated, and the portion boiling between 
50 and 60 mixed with a strong solution of 'sodium bisulphite.' 
The crystalline cake of 'acetone sodium bisulphite,' which 
separates on standing, is well pressed, to free it from impurities, 
decomposed by distillation with dilute sodium carbonate, and the 
aqueous distillate of pure acetone dehydrated over calcium chloride. 

Acetone is a colourless, mobile liquid of sp. gr. 0-792 at 20; 
it boils at 56-5, has a peculiar, ethereal odour, and is miscible 
with water, alcohol, and ether in all proportions. 

In chemical properties acetone resembles aldehyde in 
several important particulars. When shaken with a con- 
centrated aqueous solution of sodium hydrogen sulphite, 
direct combination takes place with considerable develop- 
ment of heat, and a colourless, crystalline substance, acetone 



sodium bisulphite, CH 3 .CO.CH 3 ,NaHS0 3 , 

separates. This compound is readily soluble in water, and is 
quickly decomposed by dilute acids and alkalies, acetone 
being regenerated. Acetone, like aldehyde, interacts with 
hydroxylamine in aqueous solution, forming acetoxime, 
(CH 3 ) 2 CO + NH 2 .OH = (CH 3 ) 2 C:NOH + H 2 0, 
a crystalline substance, melting at 59. When treated with 
phosphorus pentachloride, the oxygen atom in acetone is 
displaced by two atoms of chlorine, and /3-dichloropropane 
is formed, 

(CH 3 ) 2 CO + PC1 5 = (CH 3 ) 2 CC1 2 + POC1 3 ; 
on reduction, acetone is converted into secondary propyl alcohol, 

(CH 3 ) 2 CO + 2H = (CH 3 ) 2 CH.OH. 

At the same time acetone differs from- aldehyde very widely 
in one or two important respects. It does not undergo 
polymerisation, and does not reduce ammoniacal solutions of 
silver hydroxide ; it is oxidised only by moderately powerful 
agents, by which its molecule is broken up, giving acetic acid 
and carbon dioxide, 

CH 3 .COCH 3 + 40 = CH 3 .COOH + C0 2 + H 2 0. 



132 ALDEHYDES AND KETONES. 

Acetone gives the iodoform reaction (p. 96), and is employed 
for the preparation of iodoform, chloroform, and sulphonal ; 
it is also used as a solvent and in gelatinising gun-cotton in 
the manufacture of cordite (p. 282). 

Constitution. Acetone is formed when isopropyl alcohol, 

~s\CH-OH (p. 105), loses two atoms of hydrogen by 

oxidation ; for reasons similar to those which hold in the 
case of ethyl alcohol (p. 125), it seems probable that only the 
hydrogen atoms of the >CH-OH grqup take part in this 
change, which may be represented as follows, 

(CH 3 ) 2 CH.OH + = (CH 3 ) 2 C(OH) 2 = (CH 3 ) 2 CO + H 2 0. 

This view of the constitution of acetone accords well with 
its whole chemical behaviour. That it does not contain 
a hydroxyl-group is shown by the fact that acetone, unlike 
the alcohols, does not form salts with acids. That the oxygen 
atom is combined with carbon only that is, that acetone 
contains a -CO- group is shown by its behaviour with 
phosphorus pentachloride, which is similar to that of alde- 
hyde. Furthermore, the -CO- group must be united with 
two methyl -groups, as in the formula CH 3 -CO-CH 3 , because 
if it were not, acetone would be identical with propalde- 

hyde, CH 3 - CH 2 'C^TT (? 105). These facts, and many others 
which might be mentioned, show that acetone has the 
constitution p-rr/C = or (CH 3 ) 2 CO ; its characteristic 

3 

properties are determined by the presence of the divalent 
carbonyl or ketonic group >C = 0, which is contained in all 
ketones. 

The similarity in chemical behaviour between acetone and 
aldehyde is at once brought to mind on considering their 
graphic formulas ; they both contain the carbonyl-group, 

/1TT TT 

Acetone, 3 >C = Aldehyde, f; >C = ; 



ALDEHYDES AND KETONES. 133 

and therefore those changes, in which only this group 
takes part, are common to both substances. Such changes 
are, for example, interaction with hydroxylamine, behaviour 
with phosphorus pentachloride, and direct combination with 
hydrogen, sodium bisulphite, &c. ; in the last two, and in 
many other reactions, acetone behaves as an unsaturated 
compound. As regards oxidation, the difference between the 
two compounds is also readily understood ; acetone does not 
contain the readily oxidisable hydrogen atom of the aldehyde 
group, and does not combine with oxygen without the mole- 
cule being broken up; it is therefore less readily acted on 
than aldehyde, and does not reduce silver oxide. Acetone 
and many other ketones give Schiff's reaction, but the 
colour usually reappears more slowly than with aldehydes ; 
by far the best means of distinguishing between an aldehyde 
and a ketone is to study the behaviour of the compound on 
oxidation (p. 142). 

Condensation of Acetone. When acetone is treated with 
certain dehydrating agents it undergoes peculiar changes, 
two or more molecules combining together with elimination 
of one or more molecules of water, 

2(CH 3 ) 2 CO = C 6 H 10 + H 2 3(CH 3 ) 2 CO = C 9 H 14 + 2H 2 0. 

Mesityl Oxide. Phorone. 

These, and similar changes, in which two or more molecules of 
the same or of different substances combine, with separation 
of water, are termed condensations, and the substances formed, 
condensation products ; the process differs from polymerisa- 
tion in this, that water is eliminated. Acetone yields three 
interesting condensation products. When it is saturated with 
dry hydrogen chloride, and the solution kept for some time, a 
mixture of mesityl oxide and phorone is formed, in accordance 
with the above equations; but when distilled with concen- 
trated sulphuric acid, acetone yields a hydrocarbon, mesitylene, 
(Part II. p, 348), a derivative of benzene, 

3(CH 3 ) 2 CO = C 9 H 12 + 3H 2 0. 



134 ALDEHYDES AND KETONES, 

Mesityl Oxide, C 6 H 10 O, is a colourless oil, boiling at 130, and 
having a strong peppermint-like smell ; when boiled with dilute 
sulphuric acid, it is decomposed with regeneration of acetone. Its con- 

CH 
stitution may be represented by the formula CH 3 -CO-CH:C<CQjj 3 . 

Phorone, C 9 H 14 O, crystallises in almost colourless prisms, 
melting at 28 ; it boils at 196, has a pleasant aromatic odour, and 
is decomposed by boiling dilute sulphuric acid with formation of 
acetone. 

Substitution Products of Acetone. Acetone is readily attacked 
by chlorine with formation of monochloracetone, CH 3 -CO-CH 2 C1 
(b.p. 119), and asymmetrical dichloracetone, CH 3 -CO-CHC1 2 
(b.p. 120). Symmetrical dichloracetone, CH^C1-CO-CH,1, is 
produced by the oxidation of dichlorisopropyl alcohol, or dichloro- 
hydrin (p. 257), CH 2 C1-CH(OH).CH 2 C1 ; it is a colourless, 
crystalline solid (m.p. 45; b.p. 172-5). Higher substitution 
products of acetone have been obtained by indirect methods. The 
final product, hexachloracetone, or per chlor acetone, CC1 3 -CO-CC1 3 , 
is a colourless liquid, boiling at 204. Corresponding bromo-sub- 
stitution products of acetone have also been prepared. 

These halogen substitution products are characterised by their 
exceedingly irritating action on the eyes, the presence of a mere 
trace of these substances in the air being sufficient to cause 
a copious flow of tears ; when dropped on the skin they produce 
very painful blisters. 

Homologues of Acetone may be obtained by the oxidation 
of the corresponding secondary alcohols and by the dry 
distillation of the calcium salts of the higher fatty acids ; 
they resemble acetone very closely in chemical properties. 

Hydroximes and Hydrazones. Aldehydes and ke tones 
interact readily with hydroxylamine, NH 2 -OH (p. 183), and 
with phenylhydrazine, C 6 H 5 .NH-NH 2 (Part II. p. 388), form- 
ing condensation products. This property is not only highly 
characteristic of all aldehydes and ketones, with one or two 
exceptions, but is also of the greatest value in the isolation 
and identification of the compounds in question. 

The substances formed by the action of hydroxylamine on 
aldehydes are called aldoxiffles, those obtained from ketones, 
ketoximes, the term oxime or Tiydroxime being applied to both. 
Acetaldehyde, for example, yields acetaldoxime, 



ALDEHYDES AND KETONES. 135 



CHg-CHO + JSTH 2 -OH = CH 3 .CH:N.OH + H 2 0, 

acetone giving acetoxime or dimethyl ketoxime, 

(CH 3 ) 2 CO + NH 2 .OH = (CH 3 ) 2 C:ls T .OH + H 2 0, 
the interactions being expressed by the general equation, 



These two important general reactions were discovered by 
Victor Meyer. 

The oximes are usually prepared by mixing an alcoholic solution 
of the aldehyde or ketone (2 mols.) with a very concentrated 
aqueous solution of hydroxylamine hydrochloride, NH 2 'OH,HC1 
(2 mols.), and then adding sodium carbonate (1 mol.) in order to 
decompose the hydrochloride and set free the base, 



The mixture is now kept at the ordinary temperature or heated 
gently for some hours, and then most of the alcohol is evaporated 
on the water-bath ; after cooling, and adding water if necessary to 
precipitate the oxime, the latter is usually deposited in crystals ; 
if not, it is extracted with ether. 

The formation of the oxime is often greatly accelerated by making 
the solution strongly alkaline with alcoholic potash (Auwers) ; in 
such cases it is usually necessary to subsequently neutralise with 
dilute sulphuric acid in order to precipitate the oxime. 

The lower aldoximes are mostly colourless, volatile, solid 
compounds, which distil without decomposing under reduced 
pressure, and mix with water in all proportions ; the higher 
members are only sparingly soluble in water. The ketoximes 
have similar properties. Many oximes are decomposed, on 
treatment with boiling moderately strong hydrochloric acid, 
with formation of hydroxylamine hydrochloride, and regenera- 
tion of the aldehyde or ketone, 
CH 3 .CH:N-OH + HC1 + H 2 = CH 3 -CHO + NH 2 -OH,HC1. 

They are usually readily soluble in caustic alkalies, with which 
they form compounds such as 

CH 3 .CH:]S T .ONa and (CH 3 ) 2 C:N-OK ; 
but they are not decomposed by alkalies, even on boiling. 



136 ALDEHYDES AND KETONES. 

One important difference between aldoximes and ketoximes is, 
that the former are decomposed by acetyl chloride, yielding cyanides 
or nit-riles (p. 294), 



whereas the latter are either converted into acetyl derivatives, 



or else undergo a peculiar intramolecular change (p. 302), giving 
alkyl-substituted amides, 

(CH 3 ) 2 C:N.OH = CH 3 .CO-NH.CH 3 . 

Acetoxiine. Metliylacetamide. 

The condensation products of aldehydes and ketones with 
phenylhydrazine were discovered by Emil Fischer, and are 
called phenylhydrazoneSj or simply hydrazones. They are 
formed according to the general equation, 



>C j + 1*2 iN-NH.C 6 H 5 = >C:N-NH.C 6 H 6 + H 2 0, 



as, for example, acetaldehyde hydrazone, CH 3 -CH:N-NH-C 6 H 6 , 
and acetone hydrazone (CH 3 ) 2 C:N-NH-C 6 H 5 . The hydra- 
zones are referred to later (Part II. p. 389), but it may be 
mentioned here that, like the hydroximes, they are usually 
decomposed by hot concentrated hydrochloric acid, with re- 
generation of the aldehyde or ketone. 

Oximes and hydrazones, especially the former, are easily 
reduced to primary amines (p. 212), a reaction of great practical 
importance. 

Cyanohydrins. Aldehydes and ketones unite directly with 
hydrogen cyanide, forming cyanohydrins, 



an important reaction which is often used in building up 
organic compounds (compare pp. 234, 248, 252). 

SUMMARY AND EXTENSION. 

The Aldehydes form a homologous series of the general formula 
C n H 2rl+r CHO, or R-CHO, and are derived from the primary 
alcohols by the removal of two atoms of hydrogen from the 
-CH 2 -OH group. The more important members of the series are 



ALDEHYDES AND KETONES. 137 

B.p. 

Formaldehyde, CH 2 H-CHO -21 

Acetaldehyde, C 2 H 4 O CH 3 -CHO +20-8 

Propaldehyde, C 3 H 6 O CH 3 .CH 2 -CHO 49 

Butaldehyde, ) /CH 3 -CH 2 .CHo-CHO 74 

Isobutaldehyde, J ^^u... \ (C H 3 ) 2 CH.CHO 63 

Valeraldehyde, \ r TT n /CH 3 -CH 2 .CH 2 .CH 2 .CHO 102 

5 10 



IsovaleraldehydeJ \(CH 3 ) 2 CH.CH 2 -CHO 92 

Capraldehyde, C 6 H 12 O CH 3 -CH 2 -CH 2 .CH 2 -CH 2 .CHO... 128 

rieptaiueiiycie, 1 c* TJ r\ OTT rf'TT i r^wo* i KX 

or (Enanthol, / C7Hl4 Wrf*** 

The Ketones are derived from the secondary alcohols by the 
removal of two atoms of hydrogen from the ^>CH-OH group, and 
have the general formula R-CO-R', where R and R' may be the 
same or different radicles ; in the former case the substance is a 
simple ketone, but when R and R' are different, it is a mixed 
ketone (compare ethers, p. 115). The more important ketones are 

Acetone, or dimethyl ketone (CH 3 ) 2 CO B.p. 56-5* 

Propione, or diethyl ketone (C 2 H 5 ) 2 CO .. 103 

Butyrone, or dipropyl ketone \ (C H ) CO -f " 144 

Isobutyrone, or di-isopropyl ketone/ 3 \ n 125 

(Enanthone, or dihexyl ketone (C 6 H 13 ) 2 CO M.p. 30-5 

Laurone (C n H 23 ) 2 CO .. 69 

Palmitone (C 15 H 31 ) 2 CO 83 

Stearone (C 17 H 35 ) 2 CO 88 

When the less important mixed ketones are also considered, the 
ketones form a homologous series, 

C 3 H 6 O, C 4 H 8 O, C S H 10 0, C 6 H 12 O, &c., 

in which numerous cases of isomerism occur. The first two 
members, acetone, CH 3 -CO/CH 3 , and methylethyl ketone, 
CH 3 .CO-CH 2 -CH 3 , exist in only one form, but there are three 
ketones of the composition C 5 H 10 O, namely, 

Diethyl Ketone or Propione. Methylpropyl Ketone. Methylisopropyl Ketone. 

CH 3 .CH 2 -CO.CH 2 .CH 3 CH 3 -CO-CH 2 -CH 2 .CH 3 CH 3 -CO-CH< 3 , 

and the number of possible isomerides rapidly increases on passing 
up the series. 

Both aldehydes and ketones may be regarded as derived from 
the paraffins, by substituting one atom of oxygen for two atoms of 

* [CH 2 ] 5 is a convenient way of writing -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -. 



138 ALDEHYDES AND KETONES. 

hydrogen ; they are, therefore, isomeric. In the case of aldehydes, 
two atoms of hydrogen of one of the CH 3 - groups in the paraffin are 
displaced, 

CH 3 .CH 2 .CH 2 .CH 3 , giving CH 3 .CH 2 .CH 2 .CHO ; 

but in the case of ketones, the oxygen atom is substituted for two 
hydrogen atoms of a -CH 2 - group, 

CH 3 .CH 2 .CH 2 .CH 3 , giving CH 3 .CH 2 .CO-CH 3 . 

Nomenclature. -The aldehydes (from alcohol dehydrogen&tum) 
are conveniently named after the fatty acids which they yield 
on oxidation : 

Formaldehyde, H-CHO, giving formic acid, H-COOH. 

Acetaldehyde, CH 3 .CHO, ,, acetic acid, CH 3 -COOH. 
Propaldehyde, C 2 H 5 -CHO, propionic acid, C 2 H 5 .COOH. 

Simple ketones, having been first obtained by the dry distillation 
of a salt of a fatty acid, are usually named after that acid from 
which they are in this way obtained ; acetone, for example, from 
acetic acid, propione from propionic acid. Mixed ketones are 
named according to the alkyl groups which they contain, as exem- 
plified above in the case of the isomerides of the composition 
C 5 H 10 0. Ketones in general may also be named after the hydro- 
carbons from which they are theoretically derived, employing 
the prefix ' keto ' and a numeral, as, for example, 2-ketopropane, 

Ckg-db-dk,, and 3-ketohexane, CH 3 .CH 2 .CO.C 4 H 2 .CH 2 .C 6 H 3 . 

Methods of Preparation. Aldehydes are formed by the oxidation 
of primary alcohols, 

CH 3 .CH 2 .OH + O = CH 3 .CHO + H 2 ; 

whereas ketones are produced from secondary alcohols by similar 
treatment, 

CH 3 .CH(OH) -CH 3 + O = CH 3 .CO-CH 3 + H 2 O. 

Aldehydes may be prepared from the fatty acids by the dry 
distillation of their calcium salts with calcium formate : 



(C 3 H 7 .COO) 2 Ca + (H.COO) 2 Ca = 2C 3 H 7 .CHO + 2CaCO 3 . 

In its simplest form this reaction may be considered as being due 
to the removal of water and carbon dioxide from one molecule of 
the fatty acid and one molecule of formic acid ; thus, 



ALDEHYDES AND KETONES. 139 

Ketones may be prepared by the distillation of the calcium salts 
of the fatty acids alone, 

(CH 3 .COO) 2 Ca = CHg-CO -CH 3 + CaCO 3 . 

If a mixture of the calcium salts of two fatty acids (other than 
formic acid) be employed, a mixed ketone is formed, 

(CH 3 .COO) 2 Ca + (C 2 H 5 .COO) 2 Ca - 2CH 3 .CO -C 2 H 5 + 2CaC0 3 ; 

Calcium Acetate. Calcium Propionate. Methylethyl Ketone. 

at the same time two simple ketones (acetone and propione) are 
produced by the independent decomposition of the two salts. 

This method of formation is readily understood if, for the sake 
of simplicity, the free acids instead of their calcium salts be 
considered, 



Ketones may, in fact, be prepared by heating the higher fatty acids 
with phosphoric anhydride at about 200, 



Stearic Acid. Stearone. 

a method especially useful in the preparation of the higher ketones, 
such as laurone, palmitone, &c., which are obtained only with 
difficulty by any other method. 

A very important synthetical method for the preparation of 
ketones consists in treating acid chlorides (1 mol.) with zinc alkyl 
compounds (1 mol.) ; in the first place, an additive product is 
formed, and this, on decomposition with water, yields the ketone, 

+ Zn (C 2 H 5 ) 2 = C 2 H 5 - CG1< 



= C 2 H 5 .CO-C 2 H 5 + C 2 H 6 + ;Zn(OH) 2 + HCli. 
: 

(Compare formation of tertiary alcohols by the action of excess of 
the zinc alkyl compound, p. 108.) 

Ketones may also be prepared by the hydrolysis of ethyl aceto- 
acetate and its derivatives, a synthetical method of great practical 
importance (p. 193). 

When hydrocarbons of the acetylene series are heated with water 
at about 325, they combine directly with the elements of water, an 
aldehyde or a ketone being formed, usually the latter, according to 
the constitution of the hydrocarbon (p. 89). 

Physical Properties. Excluding formaldehyde, which is gaseous 



140 ALDEHYDES AND 

at ordinary temperatures, the aldehydes and ketones up to about 
C n H 22 are colourless, mobile, neutral, volatile liquids. Alde- 
hydes have usually a disagreeable, irritating smell, and their sp. 
gr. (at 20) varies from about 0-780 in the case of acetaldehyde to 
0-834 in the case of caprylic aldehyde, C 7 H 15 -CHO. Ketones have 
generally a rather pleasant odour, and their sp. gr. (at 20) varies 
from 0-792 in the case of acetone, to 0-830 in the case of caprone, 
(C 5 H n ) 2 CO. The boiling-point rises fairly regularly on passing 
up both series. The lower members of both classes of com- 
pounds are readily soluble in water, but the solubility rapidly 
decreases as the number of carbon atoms in the molecule 
increases. 

The higher aldehydes and ketones are usually colourless, waxy 
solids, insoluble, or nearly so, in water, but readily soluble in alcohol 
and ether. 

Chemical Properties. Aldehydes and ketones have many chemical 
properties in common, because they are similar in constitution, 
both classes of substances containing the carbonyl- group >CO. 
Owing to the presence of this group, they have the power of com- 
bining directly under certain conditions with two monad atoms or 
their valency equivalent. 

All the lower aldehydes and many* of the lower ketones form 
crystalline additive compounds when shaken with a concentrated 
aqueous solution of sodium bisulphite. This property is of great 
value in purifying aldehydes and ketones, and especially in 
separating them from substances which do not form 'bisulphite 
compounds,' as illustrated in the preparation of acetone (p. 131). 
These ' bisulphite compounds ' are soluble in water, but usually in- 
soluble, or nearly so, in alcohol and ether. They may be regarded 
as salts of hydroxy-sulphonic acids^ the compounds formed by 
aldehyde and acetone respectively being 

CH 3 -CH(OH)-S0 3 Na 3 >C(OH)-S0 2 Na. 

Sodium Hydroxyethylsulphonate. Sodium Hydroxyisopropylsulphonate. 

All these compounds are readily decomposed when warmed 
with dilute alkalies or acids, the aldehydes or ketones being 
regenerated, 

CH 3 .CH 2 .CH(OH)-S0 3 Na + HC1 = CH 3 -CH 2 .CHO + NaCl + H 2 SO 3 . 

* With few exceptions, only those ketones containing the group 
CH 3 -CO combine readily with NaHSO 3 . 

t A sulphonic acid is an organic acid containing the group S0 2 -OH 
(Part II. p. 392). 



ALDEHYDES AND KETONES. 141 

The characteristic behaviour of aldehydes and ketones with 
hydroxylamine and with phenylhydrazine has been described 
above. 

Aldehydes and ketones are readily acted on by reducing agents, 
such as sodium amalgam and water, zinc and hydrochloric acid, 
with formation of primary and secondary alcohols respectively, 



A secondary alcohol is not the sole product of the reduction of 
ketones, but is usually accompanied by varying quantities of a 
di-tertiary alcohol belonging to the class of pinacones. Acetone, 
for example, yields not only isopropyl alcohol, CH 3 -CH(OH)-CH 3 , 
but also acetone pinacone, 

2(CH 3 ) 2 CO + 2H = (CH 3 ) 2 C(OH) -C(OR)(CR^ 
The formation of a pinacone may be accounted for by assuming 

T> f^TT 

that, in the reduction of a ketone, a substance, T>^C<C > is 

momentarily produced by combination with one atom of hydro- 
gen. This hypothetical intermediate product may then combine 
with another atom of hydrogen to form a secondaiy alcohol 
T? OTT 

^>C<CTT or two molecules may unite to form a pinacone, 

IV -tl 



, 

D ^>C -- C-^T*. Similar products (di-secondary alcohols) are 
K .K 

formed in the reduction of aldehydes, but in smaller quantities. 

Pinacone is decomposed on distillation with dilute sulphuric acid, 
yielding pinacoline, 



a very remarkable change, which involves the migration (the removal 
from one part of the molecule to another) of a methyl -group. 
Pinacoline is a colourless liquid, boils at 106, and has a very strong 
odour of peppermint. That it has the constitution given above is 
shown by the facts that on oxidation with chromic acid it yields 
trimethylacetic acid and carbon dioxide, 

(CH 3 ) 3 C.CO .CH 3 + 40 = (CH 3 ) 3 C.COOH + C0 2 + H 2 0, 

and that it is formed by the action of zinc methyl on trimethyl- 
acetyl chloride, (CH 3 ) 3 .COC1. (Compare p. 139.) 

Aldehydes and ketones are readily acted on by phosphorus penta- 
chloride or pentabromide with formation of dihalogen derivatives of 



142 ALDEHYDES AND KETONES. 

the paraffins, the oxygen atom of the >CO group being displaced 
by two atoms of halogen. Aldehyde, for example, gives a dichlor- 
ethane or ethylidene chloride, CH 3 .CHC1 2 , an4 a dibromethane or 
ethylidene bromide, CH 3 .CHBr 2 ,* 

CH 3 .CHO + PC1 5 = CH 3 .CHC1 2 + POC1 3 , 
and acetone gives fi-dichloropropane or acetone dichloride, 

(CH 3 ) 2 CO + PC1 5 = (CH 3 ) 2 CC1 2 + POC1 3 . 

Aldehydes and ketones combine directly with hydrogen cyanide, 
forming additive products, termed hydroxycyanides or cyanohydrins. 
This reaction may be expressed by the general equation, 



aldehyde, for example, giving hydroxyethyl cyanide or aldehyde 
cyanohydrin, CH^CH(OH)-CN, and acetone, hydroxyisopropyl 
cyanide or acetone cyanohydrin, (CH 3 ) 2 C(OH)-CN. These com- 
pounds are decomposed by alkalies into their constituents, but 
mineral acids hydrolyse them, yielding hydroxycarboxylic acids, 
the -CN group being transformed into -COOH (compare p. 287), 
CH 3 .CH(OH).CN +2H 2 = CH 3 .CH(OH)-COOH + NH 3 . 

Aldehydes differ from ketones in the following important respects : 
They usually undergo oxidation to a fatty acid on exposure to the 
air, and are readily oxidised by an ammoniacal solution of silver 
hydroxide, especially in presence of a little potash or soda, a silver 
mirror being formed. They also reduce alkaline solutions of copper 
(Fehling's solution, p. 268). Ketones, on the other hand, are only 
attacked by powerful oxidising agents, and the difference between 
their behaviour on oxidation and that of aldehydes is so charac- 
teristic that it may be made use of for determining Avhether a 
substance of doubtful constitution be an aldehyde or a ketone. 

Aldehydes, on oxidation, are converted into fatty acids containing 
the same number of carbon atoms, 

CH 3 .CH 2 .CHO + O = CH 3 .CH 2 .COOH, 

Propaldehyde. Propionic Acid. 

CH 3 .[CH 2 ] 5 .CHO + O = CH 3 .[CH 2 ] 5 .COOH. 

Heptaldeliyde. Heptylic Acid. 

Ketones, on oxidation, are decomposed with formation, usually, of 
a mixture of acids, each of which contains a smaller number of 
carbon atoms than the original ketone, 

CH 3 -CO.CH 3 + 40 = CH 3 -COOH + CO 2 + H 2 O. 
CH 3 .CO.;[CH 2 ] 4 .CH 3 + 30 = CH 3 -COOH + CH 3 .[CH 2 ] 3 .COOH. 

* The divalent group CH 3 -CH< is termed ethylidene. 



ALDEHYDES AND KETONE8. 143 

In the case of mixed ketones, several acids may be formed. 
Methylamyl ketone, for example, might yield acetic acid and 
valeric acid on oxidation, in which case the molecule would be 
decomposed as indicated by the dotted line in the above equation, 
or it might give carbon dioxide and caproic acid, the molecule 
being attacked in a different manner, 

CHg.JGO .[CH 2 ] 4 .CH 3 + 40 = CH 3 .[CH 2 ] 4 -COOH + H 2 + C0 2 . 

It frequently happens, therefore, that on oxidising mixed 
ketones several products are formed, the nature of which may 
afford important evidence as to the constitution of the ketone. 
Generally speaking, the oxidation of a mixed ketone follows the 
rule (Popoff 's law) that the ketonic group -CO- remains united with 
the smaller alkyl - group, in which case the decomposition repre- 
sented in the above example by the first equation would take place 
almost entirely. Later experiments have shown, however, that 
Popoff 's rule does not hold good in all cases, and must be con- 
sidered as only approximately correct. 

Aldehydes differ from ketones in combining readily with am- 
monia, forming additive products, 



These compounds, of which aldehyde ammonia is an example, are 
usually crystalline, and very readily soluble in water. They are 
decomposed on distillation with dilute acids, with regeneration of 
the aldehyde, 

R.CH<^ + HC1 = R.CHO + NH 4 C1. 

Aldehydes differ again from ketones in combining directly with 
alcohols with elimination of water, to form substances called 
acetals, 



Aldehydes, especially the lower members of the series, very 
readily undergo polymerisation, a property which distinguishes 
them from ketones in a very striking manner. Polymerisation 
may take place spontaneously, as in the case of formaldehyde, but 
usually only on addition of a small quantity of some mineral acid 
or of some substance, such as ZnCl 2 , SO 2 , &c., which acts in a 
manner as yet unexplained. The most common form of polymer- 
isation is the combination of three molecules of the aldehyde to 
form substances such as.trioxymethylene, (CtLO)^ and paracetalde- 



144 ALDEHYDES AND KETONES. 

hyde, (C 2 H 4 0) 3 , the constitutions of which are probably respectively 
represented by the formulae, 

O , O / 



H-CH/ CH-H CH 3 -CH, CH-CH 3 



H . CH 



Trioxymethylene. Paracetaldehyde, or Paraldehyde. 

The method of combination of the three unsaturated molecules 
to form a polymeride will be readily understood with the aid of the 
dotted lines. These polymerides are decomposed into the original 
aldehydes on distillation with water or acids. They do not show 
the characteristic reactions of aldehydes because they do not 
contain the aldehyde group ; the misleading names paraldehyde, 
metaformaldehyde, &c., were given to such substances when 
their constitutions were unknown. 

Aldehydes are generally very unstable in presence of alkalies, by 
which they are converted into brown resins of unknown nature. 

Ketones, as mentioned above, are much more stable than alde- 
hydes ; they do not reduce alkaline solutions of silver, copper, &c., 
nor combine directly with ammonia or with alcohols, and they do 
not polymerise like the aldehydes. 

When treated with dehydrating agents, both aldehydes and 
ketones readily undergo condensation, two or more molecules 
combining with loss of water, as illustrated in the case of aldehyde 
(p. 126) and acetone (p. 133). When condensations of this nature 
take place, the hydrogen atoms of one of the -CH 2 - or CH 3 - 
groups, which is in direct combination with the >CO group, are 
invariably eliminated, as shown in the following schemes, in which 
R, R' may be either hydrogen atoms or similar or different alkyl 
groups : 

R.C;H 2 ;.CO.R') R-C-CO-R' 

V = II (Type of Mesityl Oxide). 

R'.CiO j.CH 2 .R) R'.fc.CH 2 .R 



R.C;H 2 ;.co.R' i 

R'-C;0 !-CiH 2 :] 
R-CH 2 .C;O !] 



R.C-CO-R' 



= R'-C-C.R (Type of Phorone). 



R-CH .( 






THE FATTY ACIDS. 145 

It is not necessary that the molecules undergoing condensation be 
identical; two different ketones, two different aldehydes, or an 
aldehyde and a ketone may condense together, always provided 
that the group -CH 2 -CO- be present in the molecule of one at least 
of the substances. 



CHAPTER IX. 

THE FATTY ACIDS. 

The fatty acids form a homologous series of the general 
formula C n H 2n+1 -COOH, or C n H 2n 2 ; they may be re- 
garded as derivatives of the paraffins, the alcohols, or the 
aldehydes. 

Paraffins. Alcohols. Aldehydes. Fatty Acids. 

H-CH 3 H.CH 2 .OH H-CHO H-COOH 

CH 3 .CH 3 CH 3 .CH 2 .OH CH 3 -CHO CH 3 -COOH 
C 2 H 5 -CH 3 C 2 H 5 .CH 2 .OH C 2 H 5 .CHO C 2 H 5 -COOH. 

The term 'fatty' was given to the acids of this series 
because many of the higher members occur in natural fats, 
and resemble fats in physical properties. 

Formic Acid, CH 2 2 , or H-COOH, occurs in nature in 
nettles, ants (formicce), and other living organisms; the 
sting of ants and nettles owes part, at least, of its irritating 
effect to the presence of formic acid. When nettles or ants are 
macerated with water and the mixture distilled, weak aqueous 
formic acid collects in the receiver. 

Formic acid can be obtained from its elements by simple 
methods. When a large flask is moistened all over on the 
inside with a concentrated solution of potash, then filled with 
carbon monoxide and heated in boiling water, the gas is slowly 
absorbed (as can be demonstrated by connecting the flask 
with a pressure-gauge) and potassium formate is produced, 

CO + KOH = H.COOK. 

When moist carbon dioxide is left in contact with potassium, 
formate and bicarbonate of potassium are formed, the carbon 

Org. J 



146 THE FATTY ACIDS. 

dioxide being reduced by the nascent hydrogen evolved 
during the interaction of the potassium and water, 



C0 2 + 2H + KOH = H.COOK + H 2 0, 
or 4C0 2 + 4K + 2H 2 = 2H-COOK + 2KHC0 3 . 

The acid may be obtained from the potassium salt by dis- 
tilling with dilute sulphuric acid. 

Formic acid can also be obtained by oxidising methyl 
alcohol or formaldehyde with platinum black (precipitated 
platinum), 

CH 3 .OH + 20 = H-COOH + H 2 H-CHO + - H-COOH, 
by heating hydrocyanic acid with alkalies or mineral acids, 

HCN + 2H 2 = H-COOH + NH 3 ,* 

and by decomposing chloroform with alcoholic potash 
(p. 176). 

Formic acid is prepared by heating oxalic acid with glycerol 
(glycerin) ; it can be obtained by heating oxalic acid alone, 



but when this is done a large proportion of the oxalic acid 
either sublimes without change or is decomposed into carbon 
monoxide, carbon dioxide, and water. 

Glycerol (about 50 c.c.) is placed in a retort connected 
with a condenser, crystallised oxalic acid (about 30 grams) 
added, and the mixture heated to about 100-110; rather 
below this temperature, evolution of carbon dioxide com- 
mences, and dilute formic acid distils, but after keeping for 
some time at 100-110 action ceases. A further quantity of 
oxalic acid is then added, and the heating continued, when 
carbon dioxide is again evolved, and a more concentrated 
solution of formic acid collects in the receiver. By adding 
more oxalic acid from time to time, a large quantity of formic 
acid can be obtained, the glycerol, like the sulphuric acid in 

* If an alkali be used ammonia is liberated, and a salt of formic acid 
obtained ; whereas when a mineral acid is employed, free formic acid and 
an ammonium salt are produced. 



THE FATTY ACIDS. 147 

the manufacture of ether (p. 113), being able, theoretically, to 
convert an unlimited quantity of oxalic into formic acid. 

When crystallised oxalic acid, C 2 O 4 H 2 + 2H 2 0, is heated with 
glycerol it loses its water of crystallisation ; the anhydrous acid is 
then decomposed into carbon dioxide and formic acid ; part of the 
latter distils with the water, part combining with the hydroxide, 
glycerol, to form the salt, glycerol formate, or monoformm, 
C 2 4 H ,2H 2 O = H-COOH + CO 2 + 2H 2 O 
C 3 H 5 (OH) 3 + H-COOH = C 3 H 5 (OH) 2 .O-CHO + H 2 O. 

On adding more crystallised oxalic acid, the monoformm is decom- 
posed by part of the water expelled from the oxalic acid crystals, 
yielding glycerol and formic acid, 

C 3 H 5 (OH) 2 .0-CHO + H 2 = C 3 H 5 (OH) 3 + H-COOH. 

The regenerated glycerol and the anhydrous oxalic acid then 
interact as before, yielding monoformin, carbon dioxide, and water. 

In order to prepare anhydrous formic acid, the aqueous distillate 
is first gently warmed with excess of litharge and then heated to 
boiling ; as soon as the litharge ceases to be dissolved, the solution 
is filtered hot, and the filtrate evaporated to a small bulk, when 
colourless crystals of lead formate are obtained, 

2H.COOH + PbO = (H.COO) 2 Pb4-H 2 O. 

This salt is carefully dried, and about |$ths of it introduced in 
the form of coarse powder, between plugs of cotton wool, into the 
inner tube of an upright Liebig's condenser, which is heated by 
passing steam through the outer tube; carefully dried hydrogen 
sulphide is then led over it, when anhydrous formic acid collects in 
the receiver, 



This is now placed in a retort connected with a condenser, the 
remainder of the dried lead salt added, and, after warming gently 
for a short time, the acid is distilled, care being taken to prevent 
absorption of moisture ; this rectification or distillation over lead 
formate is necessary in order to free the acid from hydrogen 
sulphide. 

Formic acid is a colourless, mobile, hygroscopic liquid of 
sp. gr. 1-241 at 0; it solidifies at low temperatures, melting 
again at 8, and boiling at 101. It has a pungent, irritating 
odour, recalling that of sulphur dioxide, and it blisters the 
skin like a nettle sting; it is miscible with water and 
alcohol in all proportions. Formic acid shows an acid reaction 



148 THE FATTY ACIDS. 

with litmus, decomposes carbonates, and dissolves certain 
metallic oxides; it behaves, in fact, like a weak mineral 
acid. Like the aldehydes, it has reducing properties, and 
precipitates silver from warm solutions of ammoniacal silver 
hydroxide, being itself oxidised to carbon dioxide, 
H-COOH + Ag 2 - 2Ag + C0 2 + H 2 0. 

"When mixed with concentrated sulphuric acid, it is rapidly 
decomposed into carbon monoxide and water, 
H.COOH = CO + H 2 0, 

and when heated alone at 160 in closed vessels, it yields 
carbon dioxide and hydrogen, 

H-COOH = C 



The Formates, or salts of formic acid, are prepared by 
neutralising the acid with alkalies, hydroxides, &c., or by 
double decomposition ; they are all soluble in water, but 
some, such as the lead and silver salts, only moderately easily; 
they are all decomposed by warm concentrated sulphuric acid, 
with evolution of carbon monoxide, and by dilute mineral 
acids, yielding formic acid. The sodium salt, H-COONa, and 
the potassium salt, H-COOK, are deliquescent; when heated 
at about 250, they are converted into oxalates with evolution 
of hydrogen, a reaction which may be made use of for the 
preparation of pure hydrogen, 

2H-COONa - C 2 4 Na 2 + H 2 . 

When ammonium formate is heated alone at about 230, it 
is converted into formamide (p. 165), but when heated with 
phosphorus pentoxide it gives hydrogen cyanide (p. 288), 
water being eliminated in both stages, 

H-COONH 4 = H.CO-NHa + H 2 

H-CO.NH 2 = HCK + H 2 0, 

Silver formate, H-COOAg, is precipitated in colourless 
crystals on adding silver nitrate to a neutral concentrated 
solution of a formate, but it is unstable, and quickly darkens 
on exposure to light, very rapidly on heating. 



THE FATTY ACIDS. 149 

In order to test for formic acid or a formate, the solution, if 
acid, is neutralised with soda, and a portion warmed with an 
ammoniacal solution of silver nitrate ; if a black precipitate 
of silver be produced, the presence of formic acid is confirmed 
by evaporating the rest of the neutral solution to dryness, 
and then warming the residue very gently with concentrated 
sulphuric acid, when carbon monoxide is evolved, and may be 
ignited at the mouth of the test tube. 

Constitution. Formic acid is produced from methyl alcohol, 
CH 3 - H, by the substitution of one atom of oxygen 
for two atoms of hydrogen, and must, therefore, have the 
constitution, 

H 

0=i-0-H . 



because these are the only formulae which can be constructed, 
assuming, as usual, that the atoms have the indicated valencies. 
But the second formula does not correctly indicate the be- 
haviour of formic acid ; it represents the two hydrogen atoms 
as being in the same state of combination, which is very 
improbable, since one of them is, the other is not, readily 
displaced by metals ; it does not recall the fact that formic 
acid behaves in some respects like an aldehyde, which is 
indicated in the first formula by the presence of the aldehyde 
H 

group = C . For these and other reasons, which will be 
seen more clearly after considering the case of acetic acid 
(p. 155), the constitution of formic acid is represented by the 
first formula, which is usually written H-CO-OH, or simply 
H-COOH. From analogy with methyl alcohol and other 
compounds, it may be assumed that it is the hydrogen atom 
of the HO- group, and not that directly combined with 
carbon, which is displaced when the acid forms salts. 

Acetic Acid, C 2 H 4 2 , or CH 3 -COOH, occurs in nature in 
combination with alcohols in the essences or odoriferous oils 



150 THE FATTY ACIDS. 

of many plants, and is formed during the decay of many 
organic substances. It can be produced by gently heating 
sodium methoxide in an atmosphere of carbon monoxide at 
about 180, just as formic acid may be obtained from sodium 
or potassium hydroxide under similar conditions, 

CH 3 .ONa + CO = CHg-COONa ; 

also by boiling methyl cyanide (p. 294) with alkalies or 
mineral acids, 

CHg-ON" + 2H 2 = CHg-COOH + 1S T H 3 ; 

and by exposing alcohol or aldehyde, in contact with platinum 
black, to the oxidising action of the air, 

C 2 H 6 + 20 = C 2 H 4 2 + H 2 C 2 H 4 + = C 2 H 4 2 . 

Acetic acid is prepared on the large scale from the brown 
aqueous distillate known as pyroligneous acid, which is 
obtained by the destructive distillation of wood (p. 90). 

This liquid is first distilled and the vapours passed through milk 
of lime, as already described, to separate the methyl alcohol, 
acetone, and other volatile neutral substances, and the solution 
of calcium acetate is then evaporated in iron pans, when tarry or 
' empyreumatic ' matter rises as a scum and is skimmed off. The 
solution is finally evaporated to dryness, and the calcium salt 
distilled with concentrated hydrochloric acid from copper vessels, 
care being taken not to employ excess of acid, 

(C 2 H 3 2 ) 2 Ca + 2HC1 = 2C 2 H 4 O 2 + CaCl 2 . 

The concentrated aqueous acetic acid which collects in the 
receiver is now mixed with a little potassium permanganate or 
dichromate, and again distilled, by which means most of the 
impurities are oxidised, and commercial acetic acid is obtained. 

Vinegar. When beer, or a weak wine, such as claret, is 
left exposed to the air it soon becomes sour, the alcohol 
which it contains being converted into acetic acid, 

C 2 H 6 + 2 = C 2 H 4 2 + H 2 0. 

This change is not a simple oxidation, as represented by the 
equation, but a process of fermentation brought about by a 
living ferment, mycoderma aceti. This ferment, being in the 



THE FATTY ACIDS. 151 

atmosphere, soon finds its way into the solution, where it 
grows and multiplies, and in some way causes the alcohol to 
combine with the oxygen of the air to form acetic acid. 
Strong wines, such as port and sherry, do not turn sour on 
exposure to the air, nor does an aqueous solution of pure 
alcohol, no matter how dilute, because the ferment is killed 
by strong alcohol, and cannot live in pure aqueous alcohol, 
since the latter does not contain nitrogenous substances, 
mineral salts, &c., which the ferment requires for food, and 
which are present in beers and wines. 

Vinegar is simply a dilute solution of acetic acid, contain- 
ing colouring matter and other substances, obtained by the 
acetous fermentation of poor wine or wine residues, of beer 
which has turned sour, and of other dilute alcoholic liquids ; 
it is manufactured by one of the two following processes. 

In the old French or Orleans process, a small quantity of 
wine is placed in large vats covered with perforated lids, the 
vats having been previously soaked inside with hot vinegar ; 
the ferment soon gets into the wine, and vinegar is produced, 
the solution gradually becoming coated with a slimy film, 
known as ' mother-of-vinegar,' which is simply a mass of the 
living ferment. After some time more wine is added, the 
process being repeated at intervals until the vat is about half- 
full j most of the vinegar is then drawn off, and the opera- 
tions repeated with fresh quantities of wine. 

In the modern German or * quick vinegar process? large 
vats, provided with perforated sides, and fitted near the top 
and bottom with perforated discs, are employed, the space 
between the discs being filled with beech-wood shavings, 
which are first moistened with vinegar in order that they 
may become coated with a growth of the ferment; diluted 
'raw-spirit,' containing 6-10 per cent, of alcohol, mixed with 
about 20 per cent, of vinegar, or with beer, or malt extract, 
to provide food for the ferment, is then poured in at the 
top, when it slowly trickles through the shavings in contact 
with the ferment, and provided with a free supply of air. 



152 THE FATTY ACIDS. 

The liquid which collects at the bottom is again poured over 
the shavings, the operations being continued until it is con- 
verted into vinegar that is to say, until almost the whole of 
the alcohol has been oxidised to acetic acid. This process is 
much more rapid than the French method, since oxidation is 
hastened by the exposure of a large surface of the liquid ; in 
both processes the fermenting liquid must be kept at a tem- 
perature of 25-40. 

Vinegar produced by the French process contains 6-10 per 
cent, of acetic acid ; whereas that produced by the German 
process from diluted raw-spirit contains only 4-6 per cent, of 
acetic acid. Vinegar is used for table purposes and in the 
manufacture of white-lead and verdigris (see below) ; it is too 
dilute to be economically employed for the preparation of 
commercial acetic acid. 

Pure acetic acid is prepared by distilling anhydrous sodium 
acetate with concentrated sulphuric acid j this salt is obtained 
by neutralising the impure commercial acid with sodium car- 
bonate, recrystallising, and then fusing to expel the water of 
crystallisation. The distillate from this process contains only 
a small quantity of water, and solidifies, when cooled, to a 
mass of colourless crystals ; it is then termed glacial acetic 
acid in contradistinction to the weaker acid, which does not 
crystallise so readily. The small quantity of water in glacial 
acetic acid can be got rid of by separating the crystals from 
the more dilute mother-liquors by pressure, melting them, and 
then cooling and filtering again, repeating the processes if 
necessary. 

Anhydrous acetic acid is a colourless, crystalline, hygro- 
scopic solid, melts at 16-5, boils at 118, and has the sp. gr. 
L080 at 0; it has a pungent, penetrating smell, a burning 
action on the skin, and a sharp, sour taste ; it is inflammable 
when near its boiling-point, burning with a feebly luminous 
flame. It is miscible with water, alcohol, and ether in all 
proportions, and is an excellent solvent for most organic com- 
pounds, and for many inorganic substances, such as sulphur, 



THE FATTY ACIDS. 153 

iodine, &c., which are insoluble in water. It is a fairly strong 
acid, dissolves certain metals, and acts readily on metallic 
hydroxides ; unlike formic acid, it has not reducing proper- 
ties. The pure acid does not decolourise potassium perman- 
ganate -j if impure, it will probably do so. 

Acetic acid is largely used in medicine, in chemical labora- 
tories, and in the manufacture of organic dyes, as well as for 
the preparation of many acetates of considerable commercial 
importance ; the uses of vinegar have been mentioned. 

The Acetates, or salts of acetic acid, are prepared by 
neutralising the acid with carbonates, hydroxides, &c., or by 
double decomposition; they are crystalline compounds, soluble 
in water, and decomposed by mineral acids with liberation of 
acetic acid. Sodium acetate, C 2 H 3 2 Na + 3H 2 0, is extensively 
used in the laboratory ; it melts in its water of crystallisation 
when heated, but as the water is expelled it solidifies again. 
The anhydrous salt is hygroscopic, and is used as a dehy- 
drating agent. Potassium acetate, C 2 H 3 2 K, is deliquescent. 
Ammonium acetate is gradually decomposed into acetamide 
(p. 164) and water on dry distillation, C 2 H 3 2 .]SrH 4 = 
CH 3 -CO-NH 2 + H 2 0. Silver acetate is precipitated in colour- 
less crystals on adding silver nitrate to a concentrated neutral 
solution of an acetate ; it is moderately soluble in cold water, 
and does not darken on exposure to light. Copper acetate, 
(C 2 H 3 2 ) 2 Cu + H 2 0, is obtained by dissolving cupric oxide in 
acetic acid ; it is a dark, greenish-blue substance. Verdigris 
is a blue, basic copper acetate, (C 2 H 3 2 ) 2 Cu + Cu(OH) 2 , con- 
taining water of crystallisation, and is manufactured by 
leaving sheet-copper in contact with vinegar, or with grape- 
skins, the sugars in which have undergone fermentation first 
into alcohol, then into acetic acid. When washed with 
water, part of the salt dissolves and green verdigris is 
obtained ; both these basic acetates are used as pigments. 
Copper acetate and copper arsenite unite to form a beautiful 
emerald-green, insoluble double salt, (CoH 3 2 ) 2 Cu + (As0 3 ) 2 Cu 3 , 
known as Schweinfurtvr green, Po.ris green, or emerald green. 



154 THE FATTY ACIDS. 

This substance was formerly employed in large quantities in 
colouring wall-papers, carpets, blinds, &c. ; but as its dust 
is poisonous, and as it is liable to decompose in presence 
of decaying organic matter, with evolution of hydrogen 
arsenide, its use is now almost abandoned. Lead acetate, 
or ' sugar of lead,' (C 2 H 3 2 ) 2 Pb + 3H 2 0, prepared by dis- 
solving litharge in commercial acetic acid, has a sweet 
(sugary) astringent taste, and is very poisonous ; when its 
solution is boiled with litharge a soluble basic lead acetate is 
formed. Ferric acetate is prepared on the large scale by dis- 
solving scrap iron in pyroligneous acid, the greenish ferrous 
salt first produced being rapidly oxidised in contact with the 
air and excess of acetic acid to the deep reddish-brown ferric 
salt; the solution is known in commerce as pyrolignite of 
iron, 'iron liquor,' or 'black liquor.' When a solution of 
ferric acetate containing traces of other salts is heated, an 
insoluble basic iron salt is precipitated, the solution becoming 
clear ; this property is made use of in separating the metals 
of the iron group, also in dyeing and 'printing' cotton, for 
which purpose ' iron liquor ' is used as a mordant, principally 
in dyeing silk and cotton black. Aluminium acetate is pre- 
pared by precipitating a solution of aluminium sulphate with 
sugar of lead, or calcium acetate, or by dissolving precipitated 
aluminium hydroxide in acetic acid ; its solution is known as 
'red liquor,'* and is used as a mordant, as when heated 
it loses acetic acid, an insoluble basic salt being formed. 
Chromic acetate is prepared by similar methods, and is also 
used as a mordant. 

If a solution is to be tested for acetic acid or an acetate, 
it is boiled with a few drops of strong sulphuric acid, when 
the characteristic smell of acetic acid is observed. A fresh 
portion of the solution is then neutralised with soda, if 
necessary, evaporated to dryness, and the residue warmed 
with a few drops of alcohol and a little strong sulphuric 
acid, when ethyl acetate (p. 188) is formed; this substance 
* Because of its use in dyeing alizarin-reds. 



THE FATTY ACIDS. 155 

is recognised by its pleasant, fruity odour (which should be 
compared with that of alcohol and of ether). 

Constitution. The formation of acetic acid by the oxida- 
tion of ethyl alcohol is clearly a process similar to that 
by which formic acid is produced from methyl alcohol ; 
if, therefore, the two changes be represented in a similar 
manner, 

H.CH 2 -OH + 20 = H-CO-OH + H 2 
CH 3 .CH 2 .OH + 20 = CHg.COOH + H 2 0, 

the constitution of acetic acid will be expressed by the 

H 

I ^O 
formula CHg-CO-OH, or H-C Of 

| MJH. 

H 

Again, formic acid is produced when hydrogen cyanide is 
boiled with mineral acids (p. 146), whilst acetic acid is formed 
from methyl cyanide under the same conditions. Expressing 
these two changes in a similar manner, 

H-CN + 2H 2 = H-CO-OH + NH 3 
CH 3 -CN + 2H 2 = CH 3 .CO-OH + NH 3 , 

the constitution of acetic acid will be represented by the 
same formula as before. 

If now other methods of formation are considered, together 
with the chemical behaviour of acetic acid, including its 
various decompositions and its relations to formic acid, it 
will be seen that the above constitutional formula, and no 
other, affords a proper interpretation or summary of all the 
facts. 

From the numerous arguments which might be advanced 
in support of this statement, the following only will be 
quoted : (1) Acetic acid contains the group HO-, because its 
behaviour with phosphorus pentachloride is similar to that of 
alcohols (pp. 96, 161). (2) It contains a methyl or CH 3 - 
group that is to say, three of the four atoms of hydrogen 
in acetic acid are directly combined with carbon. This is 



156 THE FATTY ACIDS. 

shown by the fact that three of the four hydrogen atoms 
behave like those in CH 4 , C 2 H 6 , &c., and are displaceable 
by free chlorine (p. 165) ; also by the production of ethane by 
the electrolysis of potassium acetate, a change which can be 
formulated in a simple manner, only by assuming the presence 
of a CH 3 - group, 

CH 3 .COOK CH C0 2 

CH 3 -COOK CH 3 C0 2 

o a M 

Since, then, judging by its chemical behaviour, acetic acid 
contains a CH 3 - and an HO- group, it must have the 

constitution CH 3 -(X~.pT, which confirms the conclusion 

previously arrived at. 

The relation between formic and acetic acids, and their 
similarity in certain chemical properties, are also satisfactorily 
accounted for by the constitutional formulae, 



H <O 



OH and CH 
which thus confirm one another. The acids are both repre- 

sented as containing the monovalent group of atoms -C\Q-rr> 

which has not been met with in any of the neutral 
compounds yet considered ; it may be concluded, there- 
fore, that their characteristic acid properties are due 
to the presence of this group. As, moreover, aldehydes 

contain the group -C\.pp but do not contain hydrogen 

displaceable by metals, it must be the hydrogen atom of 
the HO- group which is displaced when the acids form 
salts. The particular monovalent group of atoms common to 
formic and acetic acids is named the carboxyl-gio\ip, and is 
usually written -CO -OH, or simply, for convenience, -COOH. 
Homologues of Acetic Acid. As all the higher members 
of the series of fatty acids resemble formic and acetic acids 
in chemical properties, may be produced by similar methods, 



THE FATTY ACIDS. 157 

and undergo similar changes, it is assumed that they all con- 
tain a carboxyl-group. With the exception of formic acid, 
they may, in fact, he regarded as derived from the 
paraffins, by the substitution of the monovalent carboxyl- 
group for one atom of hydrogen; acetic acid, CH 3 -COOH, 
from methane, CH 4 ; propionic acid, C 2 H 5 'COOH, from ethane ; 
and so on. They form, therefore, a homologous series of 
the general formula C M H 2M+1 -COOH, or C n H 2n 2 , and are 
all monobasic or monocarboxylic acids. 

As in other homologous series, the higher members exist in 
isomeric forms, the number of isomerides theoretically possible 
in any given case being the same as that of the corresponding 
primary alcohols. The two isomeric acids, butyric acid, 

CH 3 .CH 2 .CH 2 .COOH, and isobutyric acid, 

for example, correspond with the two primary alcohols 



CH 3 .CH 2 .CH 2 .CH 2 .OH, and 3 >CH.CH 2 .OH, respectively. 

3 

Those isomerides which are derived from the normal 
paraffins (p. 65), by substituting -COOH for one atom of 
hydrogen in the CH 3 - group, are termed normal acids, 
as normal butyric acid, CH 3 -CH 2 -CH 2 -COOH, normal 
heptylic acid, CH 3 .CH 2 .CH 2 .CH 2 .CH 2 .CH 2 .COOH; those 

f^TT \ 
which contain the group n 3 /CH- are usually termed 

^ M 3 

/~1TT 

iso-acids, as, for example, isobutyric acid, p 

"^ 

r^iT x 

iso valeric acid, ~ 3 ^CH-CH 2 -COOH, but the term is not 

used very systematically. 

With the exception of the normal acids and one or two 
well-known iso-acids, such as those just quoted, it is usual, 
to avoid confusion, to name the fatty acids as if they were 
derived from acetic acid, just as the alcohols are regarded as 
derivatives of carbinol ; the four isomerides of the molecular 
formula, C 5 H 10 2 , for example, are named as follows, 



158 THE FATTY ACTDS. 



CH 3 .CH 2 .CH 2 .CH 2 .COOH 



Normal Valeric Acid Isovaleric Acid 

(Propylacetic Acid). (Isopropylacetic Acid). 

CH 3 

>C 

X 



\ 

H.COOH 



Methylethylacetic Acid. Trimethylacetic Acid. 

Propionic acid, C 3 H 6 O 2 , or CH 3 .CH 2 .COOH, exists in 
only one form, and occurs in crude pyroligneous acid ; it is 
formed when acrylic acid (p. 263) is reduced with sodium 
amalgam and water, 



and when lactic acid (p. 231) is heated with concentrated 
hydriodic acid (p. 55), reduction taking place in two stages, 
CH 3 .CH(OH).COOH + HI = CH 3 .CHLCOOH + H 2 

CH 8 .CHLCOOH + HI = CH 8 .CH 2 -COOH + 1 2 . 
It is prepared hy oxidising propyl alcohol with chromic acid, 

CH 3 .CH 2 .CH 2 .OH + 20 = CH 3 -CH 2 .COOH + H 2 0. 
Propionic acid is a colourless liquid, boils at 141, and has a 
pungent sour smell ; it is miscible with water in all propor- 
tions, but on adding a little calcium chloride to the solu- 
tion part of the acid separates at the surface, forming an 
oily layer. This property is characteristic of all fatty acids 
which are readily soluble in water, except formic and acetic 
acids. Propionic acid is a mono-carboxylic acid, and closely 
resembles acetic acid in chemical properties; its salts, the 
propionates, are soluble in water, and of little importance. 

There are two acids of the molecular formula C^S 8 O y 
Normal butyric acid, CH 3 -CH 2 .CH 2 .COOH, occurs in the 
vegetable and animal kingdoms, both in the free state and 
in combination with glycerol ; it is an important constituent 
of butter. It is formed during the decay of nitrogenous 
animal matter, and during the butyric fermentation of lactic 
acid. When milk is left exposed to the air it turns sour, the 
lactose or milk sugar which it contains being converted into 



THE FATTY ACIDS. 159 

lactic acid by a minute organism, the lactic ferment, which 
is present in the air, and finds its way into the milk, 



Lactose. Lactic Acid. 

The lactic ferment has the power of converting other sugars 
besides lactose into lactic acid. If now a little decaying 
cheese be added to the sour milk, and the solution be kept 
neutral by adding some chalk,* butyric fermentation sets 
in, the lactic acid being converted into butyric acid by the 
action of another organism, the butyric ferment, which is 
present in the decomposing cheese, 

2C 3 H 6 3 = C 4 H 8 2 + 2C0 2 + 2H 2 . 

Butyric acid is usually prepared by a combination of these 
two processes of fermentation. 

Butyric acid is a thick sour liquid, boiling at 163. It 
has a very disagreeable odour, like that of rancid butter 
and stale perspiration, in which it occurs ; it is miscible 
with water in all proportions, but separates on adding 
calcium chloride. 

The butyrates, or salts of butyric acid, are soluble in 
water; the calcium salt (C 4 H 7 2 ) 2 Ca + H 2 is more soluble 
in cold than in hot water, so that when a cold saturated 
solution is heated, part of the salt separates in crystals, 
and the solution becomes turbid. 

Isobutyric acid, or dimethylacetic acid, (CH 3 ) 2 CH-COOH, 
may be prepared by the oxidation of isobutyl alcohol, 
(CH 3 ) 2 CH-CH 2 .OH + 20 - (CH 3 ) 2 CH-COOH + H 2 0. 

It boils at 155, and resembles the normal acid very closely, 
but is not miscible with water in all proportions, one part 
of the acid requiring above five parts of water for solution. 
The calcium salt (C 4 H r 2 ) 2 Ca + 5H 2 0, unlike that of butyric 
acid, is more soluble in hot than in cold water. 

Of the four isomerides of the molecular formula C 5 H 10 2 , 
isovaleric acid, or isopropylacetic acid, (CH 3 ) 2 CH-CH 2 -COOH, 

* The ferment ceases to act if the solution become too strongly acid. 



160 THE FATTY ACIDS. 

and optically active valeric acid, or methylethylacetic acid 
(Part II. p. 545), 



are the most important. These acids occur together in the 
plant all-heal, or valerian, and in angelica root ; the mixture 
of acids obtained by distilling the macerated plants with 
water is known as valeric or valerianic acid, and is an oily 
liquid, boiling at about 174. A mixture of these two 
acids may be prepared by oxidising commercial amyl alcohol 
(p. 106) with chromic acid. 

The hexylic acids, C 6 H 12 2 , are of little importance ; seven 
of the eight isomerides theoretically possible are known, 
including normal hexylic acid (caproic acid). 

Normal heptylic acid, C 7 H 14 2 , or C 6 H 13 -COOH, one of 
the seventeen theoretically possible isomerides, of which 
only nine are known, is prepared by oxidising castor-oil, or 
cenaiithaldehyde (p. 129), with nitric acid ; it is an oily, 
rather unpleasant-smelling liquid, sparingly soluble in water ; 
it boils at 223, and, like all the lower members of the series, 
is readily volatile in steam. 

Palmitic acid, C 16 H 32 2 , or C 15 H 31 -COOH, and stearic acid, 
C 18 H 36 2 , or C l7 H 35 -COOH, occur in large quantities in animal 
and vegetable fats and oils (p. 169), from which they are 
prepared on the large scale principally for the manufacture 
of stearin candles ; they are colourless, waxy substances, 
melting at 62 and 69 respectively, and insoluble in water, 
but soluble in alcohol, ether, &c. Their sodium and potassium 
salts are soluble in pure water, and are the principal con- 
stituents of soaps (p. 171), but their calcium, magnesium, 
and other salts are insoluble. A mixture of these two acids 
was at one time thought to be a definite compound, and 
named margaric add; this name is now given to an arti- 
ficially prepared acid, C lY H ;34 2 , or C 16 H 33 -COOH, which stands 
between palmitic and stearic acids in the series, and which 
seems not to occur in nature. 



THE FATTY ACIDS. 161 

Derivatives of the Fatty Acids. 

Acid Chlorides. When phosphorus pentachloride is added 
to anhydrous acetic acid an energetic action takes place, and 

acetyl chloride, CH. S -C\~, is formed, with evolution of 

hydrogen chloride ; this change is analogous to that which 
occurs when an alcohol is treated with phosphorus penta- 
chloride, 

CH 3 .CO.OH + PC1 5 = CH 3 .COC1 + POC1 3 + HC1 
CH 3 .CH 2 .OH + PC1 5 = CH 3 .CH 2 C1 4- POC1 8 + HC1. 
Phosphorus trichloride and oxychloride also convert acetic 
acid into acetyl chloride. 

Acetyl chloride is easily prepared by adding phosphorus 
trichloride (4 parts) from a tap funnel to anhydrous acetic 
acid (5 parts) contained in a distillation flask connected with 
a condenser, and then distilling from a water-bath, 

3CH 3 -COOH + 2PC1 3 = 3CH 3 -COC1 + P 2 3 + 3HC1. 
Another method of preparation consists in dropping phos- 
phorus oxychloride (4 parts) on to anhydrous sodium acetate 
(15 parts), and then distilling, as before, 

2CH 3 -COONa + POC1 3 = 2CH 3 -COCl + tfaP0 3 + NaCl. 

Acetyl chloride is a colourless, pun gent- smelling liquid, boils 
at 55, and fumes in moist air ; when poured into water it is 
rapidly decomposed, with formation of acetic acid, 
CH 3 .COC1 + H 2 = CH 3 .COOH + HC1. 

Acetyl chloride bears the same relation to acetic acid as 
ethyl chloride to alcohol ; it may, in fact, be produced by 
passing hydrogen chloride into anhydrous acetic acid con- 
taining phosphorus pentoxide, which combines with the 
water formed, and thus prevents the reverse change (compare 

P- 191), 

CH 3 .COOH + HC1 - CH 3 .COC1 + H 2 0. 

Acetyl chloride is not only quickly decomposed by alkalies 
and by water, but also, more or less rapidly, by all compounds 



162 THE FATTY ACIDS. 

containing one or more liydroxyl-groups ; the interaction 
always takes place in such a way that hydrogen chloride is 

produced, the monovalent acetyl group CH 3 -C\^ displacing 
the hydrogen of the hydroxyl-group, 

C 2 H 5 -OII + CH 3 .COC1 = C 2 H 5 .O.CO-CH 3 + HC1 
C 3 H r OH + CH 3 .COC1 = C 3 H 7 .0-CO-CH 3 + HC1. 
Acetyl chloride may therefore be employed as a reagent for 
determining the presence of a hydroxyl-group. All that is 
necessary is to add the dry substance, in the state of a fine 
powder, if a solid, to excess of acetyl chloride, and then heat 
the mixture or solution for some time. The substance may 
be recovered unchanged, indicating that it is not a hydroxy- 
compound, or it may be converted into a new substance, 
an acetyl derivative, by the substitution of the acetyl-group 
for hydrogen ; in the latter case a combustion of the sub- 
stance is usually made, in order to ascertain its composition, 
from which the number of times the acetyl-group has dis- 
placed hydrogen is determined ; * or, since acetyl derivatives 
are generally decomposed by boiling acids and alkalies, the 
percentage of acetic acid obtained from the substance may be 
estimated by boiling with a known quantity of standard 
alkali or acid, and then estimating by titration the amount of 
acetic acid which has been formed, 

C 2 H 5 .O.CO.CH 3 + KOH = C 2 H 5 -OH + CH 3 .COOK. 

All the fatty acids except formic acid may be converted into 
acid chlorides, such as propionyl chloride, CH 3 -CH 2 -COC1, by the 
methods described above ; the products resemble acetyl chloride 
in chemical properties, and may Le employed for the detection 
of hydroxyl-groups. Acid bromides, such as CH 3 .COBr, can be 
obtained in a similar manner. 

Anhydrides. The hydrogen atom in a carboxyl-group 
-COOH is not, as a rule, displaced by the acetyl-group on 

* Except when the acetyl derivative has the same, or nearly the same, 
percentage composition as the original substance, in which case the 
number of acetyl-groups in the molecule is determined by the second 
method, 



THE FATTY ACIDS. 163 

treatment with acetyl chloride, but when an alkali salt of 
a fatty acid is heated with acetyl chloride an acetyl derivative 
of the acid is formed, 

CHo-COOK + CH,y COC1 = CH 3 -CO.O.CO.CH 3 + KC1. 

O O o > 

The compound obtained from an acetate in this way may 
be regarded as acetyl oxide, (CH 3 -CO) 2 0, or as an anhydride 
of acetic acid, derived from 2 mols. of the acid by loss 
of 1 mol. of water, just as ethers are derived from alcohols, 
and inorganic anhydrides from the corresponding acids, 

CH 3 -CO;OH CH 3 .COV. 

mr rTkrviT ~~ r"ir nn/ u + 1 2 u 

L/xl 3 'OvyU:Xl ^lljj'V^L/' 

C 2 H 6 -OH _ C 2 H 5 \^ , H o 

CA-OH-c^A 

Acetic anhydride, (CH 3 -CO) 2 0, may be prepared by heat- 
ing the anhydrous alkali acetates (4 rnols.) with phosphorus 
oxy chloride (1 mol.) ; the salt is first acted on by the 
oxychloride, yielding acetyl chloride (see above), which inter- 
acts with more salt, forming acetic anhydride, or, expressed 
in one equation, 

4CH 8 .COONa + POC1 3 = 2(CH 3 -CO) 2 + NaP0 3 + 3NaCl. 

Acetic anhydride is a mobile liquid, boils at 137, and has an 
unpleasant, irritating odour ; it is decomposed by alkalies, by 
water, and by all substances which contain the hydroxyl- 
group, acetyl derivatives being formed, 

(CH 3 .CO) 2 + H 2 = 2CH 3 -COOH 
(CH 3 -CO) 2 + C 2 H 5 .OH = CH 3 .CO.OC 2 H 5 + CH 3 -COOH. 

Acetic anhydride may therefore be employed in ascertaining 
whether a substance contain a hydroxyl-group just as well 
as acetyl chloride, the operations being carried out as already 
described.* 
All the fatty acids, except formic acid, may be converted into 

* The action of acetic anhydride on substances containing hydroxyl- 
groups is often accelerated by the addition of anhydrous sodium acetate, 
or of a small quantity of zinc chloride or sulphuric acid. 



164 THE FATTY ACIDS. 

anhydrides by treating the acid chloride with the alkali salt of the 
acid, or by heating excess of the alkali salt with phosphorus oxy- 
chloride. If an acid chloride be treated with a salt of a different 
acid, mixed anhydrides, corresponding with the mixed ethers, are 
obtained. All these anhydrides resemble acetic anhydride in 
chemical properties. 

Amides. Acetyl chloride and acetic anhydride interact 
not only with compounds containing a hydroxyl-group, but 
also with anhydrous ammonia; the compound obtained in 
this way may be regarded as derived from ammonia by the 
substitution of the acetyl-group for one atom of hydrogen, 
and is named acetamide, 

CHg-COCl + 2NH 3 = CH 3 .CO-NH 2 + NH 4 C1 
(CH 3 .CO) 2 + 2NH 3 = CH 3 .CONH 2 + CH 3 .CO.ONH 4 . 
Acetamide, CH 3 -CO-KH 2 , may also be produced by heat- 
ing ethyl acetate (p. 188) with concentrated aqueous ammonia 
under pressure, 

CH 3 .CO-OC 2 H 5 + NH 3 = CH 3 .CO-NH 2 + C 2 H 5 -OH, 
but it is best prepared by slowly distilling ammonium acetate 
in a stream of dry ammonia, 

CH 3 .CO.ONH 4 - CH 3 .CO-NH 2 + H 2 0. 

As one distillation is not sufficient to ensure complete decom 
position, that portion of the distillate boiling above 140 is collected 
separately and redistilled, these operations being repeated three or 
four times. 

Acetamide crystallises in colourless needles, melts at 
80-82, and boils at 222. When pure it has only a faint 
odour, but as usually prepared it has a strong smell of mice, 
owing to the presence of traces of impurity; it is readily 
soluble in water and alcohol. When heated with mineral 
acids or alkalies it is decomposed into acetic acid and 
ammonia, or their salts (compare foot-note, p. 146), 

CH 3 .CO-NH 2 + H 2 = CH 3 .COOH + NH 3 ; 
on distillation with phosphoric anhydride it loses 1 mol. of 
water, and is converted into methyl cyanide or acetonitrile, 
CH 3 .CONH 2 = CH 3 -ClSr + H 2 0. 



THE FATTY ACIDS. 16f) 

Formic acid and all the higher fatty acids may be converted into 
amides by methods similar to those given above ; fomnamide, 
H-CO'NH 2 , for example, may be prepared by distilling ammonium 
formate. These amides closely resemble acetamide in chemical 
and physical properties, but their solubility in water rapidly 
diminishes on passing up the series. It is a remarkable fact that 
the melting-points of the amides of the fatty acids lie very close 
together, most of them melting between 95 and 110, and all 
within the limits of 79 and 129. 

Halogen Substitution Products of Acetic Acid. 

Since acetic acid, like methyl chloride, is a mono-substitu- 
tion product of marsh-gas, and contains three atoms of 
hydrogen combined with carbon, it might be expected to give 
halogen substitution products, just as does methyl chloride. 
As a matter of fact, acetic acid yields three substitution pro- 
ducts when it is heated with chlorine in direct sunlight, 
CH 3 .COOH + C1 2 = CH 2 CLCOOH + HC1 
CH 3 -COOH + 2C1 2 = CHC1 2 .COOH + 2HC1 
CH 3 -COOH + 3C1 2 = CC1 3 -COOH + 3HC1. 

If the constitutions of acetic acid and of these three com- 
pounds be correctly represented by these formula, it would 
be expected that, as the chloro-substitution products still 
contain the carboxyl-group, they would behave like mono- 
carboxylic acids, and, like acetic acid, form salts, acid chlorides, 
anhydrides, &c. This again is the fact; the three substitu- 
tion products are monobasic acids, similar to acetic acid and 
to one another in chemical properties. 

The three chloracetic acids may be prepared by passing 
chlorine into boiling acetic acid, to which a little iodine has 
been added. When iodine is present the process can be 
earned out in absence of sunlight, because the iodine is 
converted into iodine trichloride, which acts on the acetic 
acid even in the dark, 

CH 3 -COOH + IC1 3 - CH 2 C1-COOH + HC1 + IC1. 

The iodine chloride is again converted into trichloride 
by direct combination with chlorine, and so the process 



166 THE PATTY ACIDS. 

continues, a very small quantity of iodine being sufficient to 
ensure chlorination. The iodine, or rather the iodine chloride, 
is spoken of as a chlorine carrier (Part II. p. 352). 

Chloracetic acid, CH 2 C1-COOH, is a crystalline substance ; 
it melts at 62, and boils at 185-187. 

Dichloracetic acid, CHC1 2 -COOH, is a liquid, and boils 
at 190-191; it is best prepared by heating chloral hydrate 
with potassium cyanide (or ferrocyanide) in aqueous solution, 

KCN + CC1 3 -CH(OH) 2 = CHC1 2 .COOH + HCN + KCL 

Trichloracetic acid, CC1 3 -COOH, is best prepared by 
oxidising the corresponding aldehyde, chloral, with concen- 
trated nitric acid, 

CClg-CHO + = CC1 3 -COOH. 

It melts at 55, boils at 195, and is decomposed by hot 
alkalies into chloroform and a carbonate, 

CClg-COOH + KOH = CHC1 3 + KHC0 3 . 

The three bromacetic and iodacetic acids are similar in pro- 
perties. On treating any of these halogen substitution products 
with nascent hydrogen, they are reconverted into acetic acid by 
inverse substitution. The higher fatty acids may be converted into 
halogen substitution products, which, however, unlike those of acetic 
acid, exist in isomeric forms. Propionic acid, for example, gives 
two monochloro-propionic acids namely, a-chloro-propionic acid, 
CH 3 .CHC1-COOH, and /3-chloro-propionic acid, CH 2 C1-CH 2 .COOH. 
For the purpose of distinguishing between these substitution pro- 
ducts, the carbon atoms are lettered a, j8, 7, 8, &c., commencing 
always with that which is combined with the carboxyl-group, 
CH 3 .CH 2 .CH 2 .CH 2 .COOH ; 

8 y /3 a 

the acid of the constitution (CH 3 ) 2 CBr-CH 2 -COOH, for example, is 
named /3-bromisopropylacetic acid. 

The fatty acids (and other saturated acids) are not readily 
attacked by any of the halogens (except perhaps by fluorine), but 
the acid chlorides and bromides, and the anhydrides, are compara- 
tively easily converted into mono -substitution products. In order 
to prepare its halogen derivative, the anhydrous acid is mixed with 
a small quantity of amorphous phosphorus, and chlorine is then 
passed into or over the mixture, or bromine is slowly added to it 



THE FATTY ACIDS. 167 

from a dropping funnel, gentle heat being afterwards applied in 
order to complete the interaction (Method of Hell and of Volhard). 
Under these conditions the acid chloride or bromide is first 
formed by the action of the halogen phosphorus compound (PC1 3 
or PBr 3 ), or the acid, if dicarboxylic (p. 234), is often converted into 
its anhydride ; substitution then takes place, the halogen dis- 
placing one hydrogen atom from the a-position ; if there be no 
hydrogen atom in the a-position, as, for example, in trimethylacetic 
acid (p. 158), a halogen derivative is not formed. When the re- 
action is at an end the product is either treated with water to 
convert it into the acid, or it is poured into an alcohol to convert 
it into an ester, 

^ >CBr.COBr + CH 3 .OH = 3 >CBr-COOCH 3 + HBr ; 

^2 H 5 ^2 H 5 

the second method is generally used when the substituted acid 
is a liquid because its ester is more easily purified by fractional 
distillation. 

Derivatives containing the halogen in other (/3, 7, &c. ) positions 
may be prepared indirectly by combining an unsaturated acid with 
a halogen acid or with a halogen (p. 263) ; also by displacing the 
hydroxyl-group of a hydroxy-acid by halogen, with the aid of a 
halogen acid (p. 246) or a halogen derivative of phosphorus. 

SUMMARY AND EXTENSION. 

The Fatty Acids. Carboxy-derivatives of the paraffins of the 
general formula CnH 2n +rCOOH, or C n H 2n 2 . The more important 
members of this homologous series are the following : 

Formic acid, H-COOH, + sV 101 1-241^0 

Acetic acid, CH 3 -COOH, +16-5 118 1-080 

Propionic acid, C 2 H 5 -COOH, -36 141 1-013 

r.Ti ^TT (Normal - 4 163 0-978 

Butyric acid, C 3 H 7 -COOH,{ Iso . _ 7go ^ Q>965 

i nu rv^TT /Normal -59 186 0-957 .. 

Valeric acid, C 4 H 9 -COOH,| Iso . _ gr m o 0>947 |( 

Heptylic acid, C 6 H 13 -COOH, Normal - 10-5 223 0-945 

Laurie acid, C n H 23 -COOH, +43-6 ' 875> | ^ 

Myristic acid, C 13 Ho 7 -COOH, ^ + 54 - 862 U| 

Palmitic acid, C^H^-COOH, +62 0-853 13 g, 

Stearic acid, C 17 H 35 -COOH, +69 0-845 J < 

It is an interesting fact that lauric acid and all the higher 
members named in this table occur in nature in fats and oils, 



168 THE FATTY ACIDS. 

contain an even number of carbon atoms, and are all normal acids. 
The higher normal acids containing an odd number of carbon 
atoms, C 8 H 17 -COOH, C 10 H 21 .COOH, &c., are known, but they do 
not occur in nature. 

Formic acid is prepared by heating oxalic acid with glycerol, 
acetic acid from pyroligneous acid, and by the acetous fermentation 
of alcohol, butyric acid by the butyric fermentation of lactic acid, 
and palmitic and stearic acids by the hydrolysis of glycerides 
occurring in fats and oils. 

Methods of Preparation. By the oxidation of primary alcohols 
and of aldehydes, 

C 2 H 5 .CH 2 .OH + 2O = C 2 H 5 .COOH + H 2 O 
C 6 H 13 .CHO + O = C 6 H 13 -COOH. 

By boiling alkyl cyanides with alkalies or mineral acids, 
C 2 H 5 .CN + 2H 2 = C 2 H 5 .COOH + NH 3 . 

By heating those dicarboxylic acids in which the two carboxyl- 
groups are combined with one and the same carbon atom (p. 240), 

CH 2 (COOH) 2 = CH 3 .COOH + C0 2 . 

By the hydrolysis of derivatives of ethyl acetoacetate (p. 193), 
CH 3 .CO.CH(C 3 H 7 ).COOC 2 H 5 + 2KOH = C 3 H 7 -CH 2 .COOK 



Physical Properties. At ordinary temperatures the lower 
members are liquids (except acetic acid), miscible with water, 
alcohol, and ether in all proportions. On passing up the series 
they become more oily in character, gradually lose their pungent 
smell, and become less readily soluble in water. The higher 
members, from C 10 H 20 O 2 , are solid, waxy, or fatty substances, have 
only a faint smell, and are insoluble in water, but soluble in 
alcohol and ether. They are all volatile in steam except the 
highest members, which, however, may be distilled in superheated 
steam. The first three members are specifically heavier than water, 
but the specific gravity decreases as the series is ascended (see table). 
With the exception of the highest members, they boil without de- 
composing under ordinary atmospheric pressure, the boiling-point 
rising about 19 for every addition of -CH 2 - to the molecule in the 
case of the normal acids ; the melting-point also rises, but not 
continuously, normal acids containing an odd number of carbon 
atoms melting at a lower temperature than the preceding normal 
members containing an even number of carbon atoms, 

C 12 H 24 O 2 CjgH^Og C 14 H 28 O 2 C 15 H 30 O 2 C 16 H 32 O 2 C 17 H 34 O 2 . 
43-6 40-5 54 51 62 60 



THE FATTY ACIDS. 169 

Chemical Properties. The fatty acids are very stable, and are 
only with difficulty oxidised and broken up ; nevertheless, owing to 
the presence of the carboxyl-group, they readily undergo a variety 
of double decompositions. They are all monobasic acids, but the 
acid character becomes less and less pronounced on passing up 
the series; whereas formic and acetic acids readily decompose 
carbonates, and dissolve metals and metallic hydroxides, the higher 
members, such as palmitic and stearic acids, are with difficulty 
recognised as acids by ordinary tests. The metallic salts of the 
lower members are soluble in water ; but on passing up the series 
the solubility decreases, until, in the case of the higher acids, only 
the alkali salts (soaps) are soluble. 

Fatty acids interact with alcohols, especially in presence of 
dehydrating agents, forming esters and water, 



When treated with phosphorus pentachloride, &c., they are con- 
verted into acid chlorides, 

C 2 H 5 .COOH + PC1 5 = C 2 H 5 .COC1 + POC1 3 + HC1. 
These acid chlorides interact readily with hydroxy-compounds, 
giving esters, 



on distillation with an alkali salt of a fatty acid they yield anhy- 
drides of the acids, 

C 2 H 5 .COC1 + C 2 H 5 .COOK = (C 2 H 5 .CO) 2 + KC1 ; 
and when treated with ammonia they give amides, 

CH 3 .COC1 + NH 3 =CH 3 .CO.NH 2 + HC1. 

The fatty acids yield halogen substitution products under suitable 
conditions. From certain salts of the fatty acids, ketones, alde- 
hydes, and paraffins can be prepared without difficulty, and, as 
the aldehydes and ketones are easily reduced to alcohols, which 
again are readily converted into ethers and olefines, all these com- 
pounds may be obtained from the fatty acids. 

The reactions by which a fatty acid may be converted into the 
next lower, or higher, homologue are described later (p. 205). 

Fats, Oils, Soaps, Stearin, and Butter. 

Composition of Fats and Oils. When beef or mutton suet 
is kneaded in a muslin bag in a basin of hot water the 
fat melts and passes out, leaving the membrane or tissue in 
the bag ; the melted fat solidifies on cooling, and is known 



170 THE FATTY ACIDS. 

as tallow. The fat obtained from pig suet, in a similar 
manner, is much softer, and is called lard. 

When tallow is heated with water in closed vessels under 
pressure at about 200, it is decomposed into glycerol (p. 254) 
and ' fatty ' acids ; if the mixture be now distilled in highly 
superheated steam these products pass over, the distillate 
being an aqueous solution of glycerol, at the surface of which 
floats the mixture of fatty acids. A similar decomposition 
takes place when tallow is heated with dilute sulphuric acid, 
but in this case it is not necessary to heat so strongly. 

All animal fats, such as lard, goose-fat, bone-fat, butter, 
&c., and the fatty vegetable oils, such as olive-, linseed-, rape-, 
palm-, and cotton-seed oils, which are obtained by pressing the 
seeds or fruit of certain plants, behave in a similar manner, 
and when heated with dilute sulphuric acid or with water, 
under pressure, are decomposed into glycerol and a mixture of 
acids of the C n H 2w 2 series (p. 1 45). The occurrence of these 
acids in natural fats and oils, and the fact that the higher 
members of the series resemble fats in physical properties, led 
to the use of the term * fatty acid,' which is now applied to 
all the members of the series. 

The chemical compounds of which these fats are com- 
posed were investigated by Chevreul, who showed them to be 
ethereal salts or esters (p. 174), formed, together with water, 
by the combination of the fatty acids with the alcohol, 
glycerol, which thus acts as a hydroxide or weak base. 
Glycerol is a tri-acid base, and can combine with and 
neutralise three molecules of a monobasic or monocarboxylic 
acid, forming neutral salts, just as can the tri-acid bismuth 
hydroxide, 

C 3 H 5 (OH) 3 + 3CH 3 .COOH = C 3 H 5 (O.CO-CH 3 ) 3 + 3H 2 
Bi(OH) 3 + 3HC1 = BiCl 3 + 3H 9 0. 

These ethereal salts or esters are collectively termed glycerides, 
and are named after the acids from which they are formed. 
The glyceride formed from acetic acid is called triacetin ; that 



THE PATTY ACIDS. 171 

from palmitic acid, tripalmitin ; and that from stearic acid, 
tristearin, and so on. 

Now, the chief constituents of fats and oils are tristearin 
and tripalmitin, which are solid at ordinary temperatures, 
and a liquid glyceride, triole'in, which is formed by the 
combination of glycerol with oleic add* When a fat con- 
tains a relatively large proportion of tristearin and tripalmitin, 
it is solid and comparatively hard (tallow) at ordinary tem- 
peratures; when, however, it contains a relatively large 
proportion of triolein it is soft and pasty (lard), or liquid 
(olive-oil). 

These glycerides, like other esters or ethereal salts, are 
decomposed by water and by dilute mineral acids, at moder- 
ately high temperatures, being converted into glycerol and an 
acid ; in the case of tristearin, for example, 
CH 2 .OCO.C ]7 H 35 CH 2 -OH 

CH.O.CO.C^ +3H 2 = CH-OH +3C 17 H 35 .COOH. 
CHa-O-CO-C^H^ CH 2 -OH 

Tristearin. Glycerol. Stearic Acid. 

Since fats and oils are mixtures of glycerides, they yield 
i mixtures of fatty acids. 

Soaps. When boiled with alkalies the glycerides are de- 
composed much more rapidly than by water, yielding alkali 
salts, the weak base, glycerol, being liberated, just as ammonia 
or methyl alcohol is liberated from its salts on boiling with a 
stronger base. In manufacturing soaps, a fat or oil, such as 
tallow or palm-oil, is heated in an iron pan with a small but 
sufficient quantity of caustic soda, when it is converted after 
some time into a thick, homogeneous, frothy solution, which 
contains glycerol and the sodium salts of the various acids 
which were present in the glycerides that is to say, the 
sodium salts of stearic, palmitic, and oleic acids. Some 

* Oleic acid, C^H^-COOH (p. 264), is a liquid at ordinary temperatures. 
It contains two atoms of hydrogen less than stearic acid, C 17 H 3 5-COOH, and 
is, therefore, an unsaturated acid, belonging to a different series ; its lead 
salt is soluble in ether, a property very rarely met with in other lead salts, 



172 THE FATTY ACIDS. 

common salt is now added, whereupon the sodium salts 
separate from the solution of glycerol and salt as a curd, 
because they are insoluble in salt water. The curd, after 
having been drained off and allowed to cool, slowly solidifies, 
and is then known as hard soap, which is simply a mixture 
of the sodium salts of palmitic, stearic, and oleic acids with 
water and alkali. When fats or oils are boiled with potash, 
instead of with soda, similar chemical changes take place, and 
the potassium salts of the acids are formed ; if common salt 
be now added to the solution, the potassium are partially con- 
verted into sodium salts, and a hard soap is finally obtained ; 
if, however, without adding salt, the homogeneous solution be 
allowed to cool, it sets to a jelly-like mass of soft soap, which 
is a mixture of the potassium salts of the above-named acids, 
containing glycerol and a large percentage of water. 

The decomposition of fats and oils in this way in the 
process of soap-making originally received the name saponifica- 
tion, and the fats and oils were said to be saponified. The 
term saponification was then applied generally to the analo- 
gous decomposition of other ethereal salts by alkalies (in 
spite of the fact that the products were not soaps), but the 
word hydrolysis has now to a great extent taken its place. 
Hydrolysis may be roughly defined as the decomposition 
of one compound into two or more, with fixation of the 
elements of water or of some hydroxide. The decomposition 
of glycerides by water, acids, and alkalies, and the changes 
expressed by the following equations, are examples of 
hydrolysis, 

H (p. 189) 
(p. 275) 
(p. 289). 



Stearin and Glycerol. Stearin consists principally of a 
mixture of stearic and palmitic acids, and is manufactured 
by decomposing tallow and other fats or oils with water, 
dilute sulphuric acid, or milk of lime, under pressure (see 



THE FATTY ACIDS. 173 

above). After distilling the products in a current of super- 
heated steam first acidifying with sulphuric acid, if lime 
has been used the pasty mixture of fatty acids is separated 
from the aqueous solution of glycerol, and pressed, in order 
to squeeze out as much of the liquid ole'ic acid as possible. 
The pressed mass is then gently warmed, and pressed again 
between warm plates, when a further quantity of oleic acid is 
squeezed out, together with some palmitic and stearic acids. 
The hard mass that remains is called stearin; it is mixed 
with a little paraffin to make it less brittle, and employed in 
large quantities in the manufacture of stearin candles. The 
liquid or pasty mass of oleic, palmitic, and stearic acids 
separated from the stearin is known as olem, and is employed 
for the preparation of soap. 

Glycerol (p. 254) is obtained from the aqueous distillate, 
after separating the fatty acids ; the solution is decolourised 
by filtration through charcoal, submitted to redistillation 
with superheated steam under reduced pressure, and finally 
evaporated to a syrup. 

Butter. Butter, prepared from cream, is a mixture of fat 
(about 82-5 per cent.), water (about 14-5 per cent.), and small 
quantities of casein, milk-sugar, and salts. Pure butter-fat 
contains about 92 per cent, of a mixture of tristearin, 
tripalmitin, and triolein, about 7-7 per cent, of tributyrin, 
and traces of other glycerides, and substances which impart 
flavour ; it differs from all other fats and oils, in containing a 
large proportion of tributyrin, the glyceride of butyric acid. 

Artificial butter, margarine or oleomargarine, is prepared from 
the best ox-suet, which is first freed from membrane or tissue by 
melting out the fat. After having been left to crystallise for 
about twenty-four hours at a temperature of 24, the fat is pressed 
and is thus separated into solid stearin and liquid oleomargarine. 
The latter forms a buttery mass when cooled to ordinary tempera- 
tures, but as it is not quite soft enough, it is mixed with a small 
quantity of pea-nut or sesame-oil and finally churned up with milk 
to give it a flavour. When carefully prepared it is a wholesome 
substitute for butter, and no doubt just as nutritious. 



174 ETHEREAL SALTS OR ESTERS. 

% 

CHAPTER X. 

ETHEREAL SALTS OR ESTERS. 

It has been pointed out that the alcohols behave in some 
respects like metallic hydroxides, and combine with acids, 
forming salts and water, 

C 2 H 5 .OH + HC1 = C 2 H 5 C1 + H 2 
C 2 H 5 .OH + H 2 S0 4 = C 2 H 5 .HS0 4 + H 2 
CH 3 -OH + CH 3 .COOH = CH 3 .COOCH 3 + H 2 0. 

These compounds are called ethereal salts or esters, in con- 
tradistinction to the metallic salts, 

Halogen Ethereal Salts and Halogen Derivatives of the 
Paraffins. 

The ethereal salts of the halogen acids are identical with 
the halogen mono-substitution products of the paraffins, and 
may be obtained either from the alcohols or from the 
paraffins; they form homologous series of the general 
formula, C M H 2n+1 -X where X = C1, Br, or I. 

Methyl chloride, CH 3 C1 Methyl bromide, CH 3 Br Methyl iodide, CH 3 I 
Ethyl C 2 H 5 C1 Ethyl C 2 H 5 Br Ethyl C 2 H 5 I 
Propyl C 3 H 7 C1 Propyl C 3 H 7 Br Propyl C 3 H 7 I 

The di-, tri-, <c. halogen substitution products of the 
paraffins, such as methylene dichloride, CH 2 C1 2 ; chloro- 
form, CHC1 3 j iocloform, CHI 3 ; and carbon tetrachloride, CCl^ 
cannot be regarded as ethereal salts, but, being closely 
related to the halogen ethereal salts, are conveniently con- 
sidered in this chapter. 

Methyl chloride, or chloromethane, CH 3 C1, is one of the 
four substitution products obtained on treating methane with 
chlorine in sunlight, and is formed in small quantities when 
methyl alcohol is heated with concentrated hydrochloric acid, 

CH,-OH + HC1 = CH,C1 + ELO, 



ETHEREAL SALTS OR ESTERS. 175 

It is prepared by passing hydrogen chloride into methyl 
alcohol containing anhydrous zinc chloride (Groves' process), 
as described in the case of ethyl chloride (p. 178) ; also by 
heating methyl alcohol with sodium chloride and concentrated 
sulphuric acid. 

It is a colourless gas, and liquefies at very low tempera- 
tures, boiling at -24 ; it burns with a green-edged flame, is 
moderately easily soluble in water, and when heated with 
water or dilute potash under pressure, it is converted into 
methyl alcohol, 

CH 3 C1 + H 2 = CH 3 .OH + HC1. 

Methyl chloride is employed on the large scale in the preparation 
of organic dyes, the compressed gas being also used for the artificial 
production of a low temperature ; for these purposes it is manu- 
factured by heating trimethylamine hydrochloricle (p. 211) with 
hydrochloric acid, 

N(CH 3 ) 3 , HC1 + 3HC1 = 3CH 3 C1 + NH 4 C1. 

Methylene dichloride, CH 2 C1 2 , is prepared by reducing 
chloroform with zinc and hydrochloric acid in alcoholic 
solution, 

CHC1 3 + 2H = CH 2 C1 2 + HC1 ; 

it is a colourless, heavy liquid, boiling at 41. 

Chloroform, or trichloromethane, CHC1 3 , is formed when 
methane, methyl chloride, or methylene dichloride is treated 
with chlorine in sunlight, and when many simple organic 
substances containing oxygen, such as ethyl alcohol, acetone, 
&c., are heated with bleaching powder, which acts as an 
oxidising as well as a chlorinating agent (see below). 

Chloroform may be prepared by distilling alcohol or acetone 
with bleaching powder. 

Some strong bleaching powder (about 450 grams) is made into 
a cream with about 1^ litres of water and placed in a large flask 
connected with a condenser ; alcohol, methylated spirit, or acetone 
(about 100 c.c.) is then gradually added, and the flask is cautiously 
heated on a water-bath ; a vigorous reaction usually sets in, and a 
mixture of chloroform, water, and alcohol or acetone distils. If 



176 ETHEREAL SALTS OR ESTERS. 

the operation has been successful, the chloroform collects as a 
heavy oil at the bottom of the receiver ; but if too much alcohol or 
acetone be present, the chloroform must be precipitated by adding 
water. It is then separated with the aid of a funnel, washed with 
water, shaken once or twice with a little concentrated sulphuric 
acid, which frees it from water, alcohol, &c., and redistilled from 
a water-bath. 

The changes which occur in the preparation of chloroform from 
alcohol are complex ; it is probable that aldehyde is first formed 
by oxidation, and then converted into chloral, which is decomposed 
by the calcium hydroxide present in the bleaching powder or 
produced during the reaction, yielding chloroform and calcium 
formate. When acetone is employed, trichloracetone is probably 
formed in the first place ; this compound is then decomposed by 
the calcium hydroxide, giving chloroform and calcium acetate, 



The chloroform prepared in this way is not quite pure ; the 
pure substance is best prepared by distilling chloral or chloral 
hydrate (p. 128) with caustic soda, the product being 
separated in the manner just described, 

CC1 3 .CHO + NaOH = CHC1 3 + H-COONa. 

Chloroform is a heavy, pleasant-smelling liquid of sp. gr. 
1-5 at 15, and boils at 61; when strongly heated it burns 
with a green-edged flame, but it is not inflammable at ordinary 
temperatures. It is readily decomposed by warm alcoholic 
potash, yielding potassium formate and chloride, 

CHC1 3 + 4KOH = H-COOK + 3KC1 + 2H 2 0. 
If a drop of chloroform be added to a mixture of aniline 
(Part II. p. 373) and alcoholic potash, an intensely nauseous 
smell is observed on warming gently, owing to the formation 
of phenylcarbylamine or phenylisocyanide* 

CHC1 3 + 3KOH + C 6 H 5 .NH 2 = C 6 H 5 .NC + 3KC1 + 3H 2 0. 
This reaction affords a very delicate test for chloroform and 
for aniline, and is spoken of as the carbylamine reaction 
(p. 207). 

* The experiment should be performed in a test tube, only one drop of 
aniline being employed, and the contents of the test tube should afterwards 
be carefully poured into the sink -pipe, in a draught closet if possible, 



ETHEREAL SALTS OK ESTERS. 177 

Chloroform is extensively employed in surgery as an anaes- 
thetic, its vapour when inhaled causing unconsciousness 
(Simpson). For this purpose pure chloroform must be 
employed, as the impure substance is dangerous, and pro- 
duces bad after-effects.* Pure chloroform gives no precipitate 
with silver nitrate, and does not darken when shaken with 
concentrated sulphuric acid or with strong potash. 

Carbon tetrachloride, or tetrachloromethane, CC1 4 , the 
final product of the action of chlorine on CH 4 , CH 3 C1, 
CH 2 C1 2 , and CHC1 3 , is prepared by passing chlorine into 
boiling chloroform in sunlight, or by passing chlorine into 
carbon disulphide in presence of antimony pentachloride, 
which acts as a chlorine carrier (p. 166), 

CS 2 + 3SbCl 5 = CC1 4 + S 2 C1 2 + 3SbCl 3 , 



in the latter case the sulphur dichloride is got rid of, after a 
preliminary distillation, by shaking the product with potash, the 
carbon tetrachloride being purified by redistillation. Carbon 
tetrnchloride is a very heavy, pleasant-smelling liquid, boiling 
at 76-77 ; on treatment with nascent hydrogen, it is con- 
verted into CHC1 3 , CH 2 C1 2 , CH 3 C1, and CH 4 successively, by 
inverse substitution. It is decomposed by hot alcoholic 
potash, 

CC1 4 + 4KOH = 4KC1 + C0 2 + 2H 2 0. 

The halogen ethereal salts, methyl bromide, CH 3 Br (b.p. 4-5), 
and methyl iodide, CH 3 I (b.p. 42), are prepared by methods 
similar to those employed in the case of the corresponding 
ethyl salts (see below), which they closely resemble in 
Khemical properties. 

: * In the presence of air chloroform gradually undergoes decomposition, 
especially under the influence of light, carbonyl chloride (phosgene gas, 
COCl a ) and hydrochloric acid being produced, CHC1 3 + O = COC1 2 + HC1. 
As carbonyl chloride is very poisonous, it is necessary to keep all chloro- 
form required for anaesthetic purposes in the dark, the bottle being kept 
as full as possible, so as to exclude air ; a little alcohol (up to 1 per cent.) 
is generally added in order to decompose any carbonyl chloride which 
might be formed, COC1 2 + 2C 2 H. V OH=2HC1 + CO(OC 2 H 5 ) 2 (ethyl carbonate}. 

Org. L 



178 ETHEREAL SALTS OR ESTERS. 

lodoform, or triiodomethane, CHI 3 , a halogen tri-substitu- 
tion product of methane, is closely related to chloroform, and 
may be considered here. It is formed when ethyl alcohol 
(but not methyl alcohol), acetone, aldehyde, and other simple 
organic substances containing oxygen united with a CH 3 'C= 
group are warmed with iodine and an alkali or alkali car- 
bonate ; the changes which occur are doubtless similar to 
those which take place in the preparation of chloroform. 

All ketones which contain the group CH 3 -CO- yield iodoform 
under the above conditions, the -CO- group being converted into 
-COOH, the CH 3 - group into iodoform. If bromine be used 
instead of iodine, a similar change occurs, and bromoform, CHBr 3 
(b.p. 151), separates ; this reaction is of considerable practical im- 
portance, and is often used for the conversion of a ketone into an 
acid containing one atom of carbon less than the parent substance. 

lodoform is prepared by gradually adding iodine to an 
aqueous solution of sodium carbonate containing a little 
alcohol and heated at 60-80; the precipitated iodoform is 
separated by filtration, and purified by recrystallisation from 
dilute alcohol. It crystallises in lustrous, yellow, six-sided 
plates, melts at 119, and has a peculiar, very characteristic 
odour ; it sublimes readily, and is volatile in steam. It is 
used in medicine and surgery as an antiseptic. 

Ethyl chloride, or chlorethane, C 2 H 5 C1, is formed when 
ethane is treated with chlorine in sunlight, and when alcohol 
is heated with concentrated hydrochloric acid, or treated 
with phosphorus pentachloride, or trichloride, at ordinary 
temperatures, 

C 2 H 5 .OH + PC1 5 = C 2 H 5 Cl + POC1 3 + HC1. 
Ethyl chloride is prepared by Groves' process namely, by 
passing hydrogen chloride, carefully dried with concentrated 
sulphuric acid, into a flask containing absolute alcohol, to 
which about half its weight of coarsely powdered, anhydrous 
zinc chloride has been added. 

The flask is connected with a reflux condenser (p. 190), and is 
provided with 8- safety tube. As soon as the solution is saturated 



ETHEREAL SALTS OR ESTERS. 179 

with hydrogen chloride, it is gently warmed on the water-bath, 
when ethyl chloride and alcohol pass off; the alcohol vapour is 
cooled in passing through the condenser, the liquid running back 
into the flask. The gaseous ethyl chloride now passes through 
three wash-bottles containing water, dilute potash, and concen- 
trated sulphuric acid respectively, by which means it is freed from 
hydrogen chloride, alcohol, and moisture ; the pure ethyl chloride 
is then collected in a U-tube immersed in a freezing mixture. 

In the absence of zinc chloride very little ethyl chloride is 
formed, because it is decomposed by the water produced 
during the interaction (compare p. 191), 

C 2 H 5 -OH + HC1 - C 2 H 5 C1 + H 2 0. 

Ethyl chloride may also be prepared by warming a mixture 
of absolute alcohol, concentrated sulphuric acid, and sodium 
chloride, the gas being purified and condensed in the same 
way as before j the sulphuric acid not only interacts with the 
salt, forming hydrogen chloride, but also prevents the decom- 
position of the ester by the water which is generated. 

Ethyl chloride is a colourless, very volatile liquid, boiling 
at 12-5; it burns with a greenish, smoky flame, and is only 
sparingly soluble in water, but miscible with alcohol, ether, 
&c. When heated with water or potash under pressure, it 
yields ethyl alcohol, 

C 2 H 5 C1 + H 2 = C 2 H 5 .OH + HC1 ; 

on treatment with chlorine in sunlight, it gives di-, tri-, &c. 
substitution products of ethane. It gives no immediate pre- 
cipitate with aqueous silver nitrate, but when warmed with 
an alcoholic solution of silver nitrate, silver chloride is quickly 
precipitated, ethyl nitrate remaining in solution, 
C 2 H 5 C1 + AgN0 3 = C 2 H 5 .N0 3 + AgCl. 

Ethyl bromide, or bromethane, C 2 H 5 Br, is formed when 
alcohol is heated with concentrated hydrobromic acid, or 
treated with phosphorus tribromide or pentabromide, at 
ordinary temperatures, 

C 2 H 5 .OH + PBr 5 = C 2 H 5 Br + POBr^ + HBr. 
It may be prepared by slowly dropping bromine (10 grams) 



180 ETHEREAL SALTS OB ESTERS. 

from a stoppered funnel into a mixture of alcohol (60 grams) 
and amorphous phosphorus (10 grams) contained in a dis- 
tilling-flask, connected with a condenser and immersed in 
cold water; after adding the whole of the bromine, the 
mixture is left for about an hour and then distilled, 
3C 2 H 5 - OH + P + 3Br = 3C 2 H 5 Br + H 3 P0 3 . 
A more convenient method is to add coarsely powdered 
potassium bromide (50 parts) to a cold mixture of alcohol 
(30 parts) and concentrated sulphuric acid (50 parts) and then 
distil slowly. 

The distillate from either process is shaken with dilute potash to 
free it from bromine, hydrobromic acid, and alcohol, and then 
washed by shaking with water ; after drying with calcium chloride, 
the ethyl bromide is purified by distillation. 

Ethyl bromide is a colourless, pleasant-smelling, heavy 
liquid, and boils at 38; it resembles ethyl chloride in its 
behaviour with water, potash, and silver nitrate. 

Ethyl iodide, or iodethane, C 2 H 6 I, is formed when alcohol 
is heated with concentrated hydriodic acid ; it is prepared by 
gradually adding iodine (65 grams), in small quantities at a 
time, to a mixture of alcohol (25 grams) and amorphous 
phosphorus (5 grams), and then distilling from a water-bath, 
the product being purified exactly as described in the case 
of ethyl bromide, 

3C 2 H 5 .OH + P + 31 = 3C 2 H 5 I + H 3 P0 3 . 

Ethyl iodide is a colourless, pleasant-smelling, highly refrac- 
tive, very heavy liquid, boiling at 72 ; on exposure to light 
it turns yellowish-brown, owing to the separation of traces 
of iodine, this phenomenon being observed in the case of 
nearly all organic compounds containing iodine. In chemical 
properties it closely resembles ethyl chloride and ethyl 
bromide. 

Other halogen ethereal salts or halogen mono-substitution pro- 
ducts of the paraffins, such as propyl bromide, C 3 H 7 Br, butyl 
iodide, C 4 H 9 I, &c., may be prepared by methods similar to those 
given above; they are all colourless, neutral, pleasant-smelling 



ETHEREAL SALTS OR ESTERS. 181 

liquids, as a rule specifically heavier than water, in which they 
are insoluble, or nearly so. They are slowly decomposed, or 
hydrolysed (p. 172), by boiling water and by aqueous alkalies, 
yielding the alcohols, 

C 3 H 7 Br + KOH = C 3 H 7 -OH + KBr ; 
when boiled with alcoholic potash, they are converted into defines, 

C 3 H 7 I + KOH = C 3 H 6 + KI + H 2 O. 

They do not give an immediate precipitate with an aqueous solution 
of silver nitrate ; but in alcoholic solution, especially on warming, 
a halogen silver salt is quickly precipitated, and an organic nitrate 
remains in solution, 

C 2 H 5 I + AgN0 3 = C 2 H 5 .N0 3 + Agl. 

Although these compounds closely resemble one another in chemical 
properties, their physical properties depend to a considerable extent 
on the halogen which they contain, the specific gravity and boiling- 
point losing on displacing chlorine by bromine, or bromine by iodine : 

Sp. gr. R T , Sp. gr. 

atO" atO" a>1) - 

Methyl chloride, CH :} C1 -22 Ethyl chloride, C 2 H 5 C1 0-921 12-5 

Methyl bromide, CH 3 Br 1-73 +4-5 Ethyl bromide, C 2 H 5 Br 147 39 

Methyl iodide, CH 3 I 2-33 42 Ethyl iodide, C 2 H 5 I 1-975 72 

Although the monohalogen derivatives of methane and ethane 
exist in only one form, those of propane and the higher paraffins 
show isomerism. There are, for example, two compounds of the 
molecular formula, C 3 H 7 I, corresponding with the two alcohols, 
C 3 H 7 -OH, namely, normal propyl iodide, CH 3 CH 2 -CH 2 I (b.p. 102), 
and isopropyl iodide, CH 3 -CHI-CH 3 (b.p. 89-5). The mono- 
halogen derivatives of butane exist theoretically in four isomeric 
forms, two of which, CH 3 -CH 2 -CH 2 .CH 2 X and CH 3 .CH 2 .CHX-CH 3 , 

CH 
are derived from normal butane ; the other two, pTT 3 ^>CH-CH 2 X 

and 3 >CX.CH 3 , from isobutane. 

Tertiary butyl iodide, (CH 3 ) 3 CI, has been previously mentioned. 
It may be obtained by treating isobutyl alcohol with zinc chloride 
or sulphuric acid, and then dissolving the isobutylene formed in 
this way in concentrated hydriodic acid, 

(CH 3 ) 2 CH-CH 2 .OH = (CH 3 ) 2 C: CH, + H 2 O 

(CH 3 ) 2 C:CH a + HI = (CH 3 ) 2 CI.CH 3 ; 

also by heating trimethylcarbinol with hydriodic acid, 
(CH 3 ) 3 C.OH + HI = (CH 3 ) 3 I + H 2 O. 



182 MHEBEAL SALTS OR 

It is a colourless oil, boils at 100, decomposing slightly, and is 
readily acted on l>y alkalies, being converted into isobutylene. 

Ethereal Salts of Nitric Acid. 

The esters or ethereal salts of nitric acid are formed when 
the halogen ethereal salts are warmed with silver nitrate in 
alcoholic solution, 

CH 3 I + AgN0 3 = CH 3 .N0 3 + Agl ; 

they are also produced, together with nitrites (see below), 
when the alcohols are treated with concentrated nitric acid, 

C 3 H 7 .OH + HM) 3 = C 3 H r N0 3 + H 2 0. 
Ethyl nitrate, C 2 H 5 -N0 3 , is formed when alcohol is treated 
with ordinary concentrated nitric acid, 

C 2 H 5 .OH + HN0 3 = C 2 H 5 -N0 3 + H 2 0, 

but so much heat is developed as the result of oxidation that, 
unless care be taken, the reaction becomes almost explosive 
in violence j even when the mixture is cooled, only a com- 
paratively small quantity of ethyl nitrate is produced, owing 
to the acid oxidising some of the alcohol, and being itself 
reduced to nitrous acid, which then interacts with the 
alcohol, forming ethyl nitrite. If, however, the nitric 
acid be mixed with a little urea (p. 301), a substance which 
decomposes nitrous acid, 

CO(NH 2 ) 2 + 2NO-OH = C0 2 + 3H 2 + 2N 2 , 
the reaction takes place quietly, and ethyl nitrate is the 
principal product. 

For these reasons ethyl nitrate is prepared by gradually adding 
alcohol (not more than 30 grams) to half its volume of nitric acid 
(sp. gr. 1-4), to which about 5 grams of urea have been added ; the 
mixture is then very slowly heated on a water-bath in a large retort 
provided with a condenser. The mixture of ethyl nitrate, alcohol, 
and acid which collects in the receiver is shaken with water in a 
separating funnel, the heavy oil dried with calcium chloride, and 
distilled from a water-bath. 

Ethyl nitrate is a colourless liquid of sp. gr. 1-11 at 20, 
and boils at 87 ; it has a pleasant, fruity odour, and is almost 



ETHEREAL SALTS OR ESTERS. 183 

insoluble in water, but readily soluble in alcohol, &c. It 
burns with a luminous flame, and when dropped on to a hot 
surface it sometimes explodes. It is slowly hydrolysed by 
boiling water, quickly by hot alkalies, yielding alcohol and 
nitric acid or a nitrate, 

C 2 H 5 -N0 3 + H 2 = C 2 H 5 .OH + HN0 3 . 

On reduction with tin and hydrochloric acid it yields Tiydroxyl- 
amine, 

C 2 H 5 .N0 3 + 6H = C 2 H 5 .OH + NH 2 -OH + H 2 0. 

Methyl nitrate, CH 3 -N0 3 (b.p. 66), and the higher homo- 
logues closely resemble ethyl nitrate in properties. 

Ethereal Salts of Nitrous Acid. 

The ethereal salts of nitrous acid are produced by the action 
of nitrous acid on the alcohols, 

C 2 H 5 -OH + HN0 2 = C 2 H 5 -N0 2 + H 2 0. 

They may be prepared by saturating the alcohols with the 
fumes evolved by the interaction of arsenious oxide and nitric 
acid,* or by distilling alcohol with sodium nitrite and 
sulphuric acid, or with copper and nitric acid.f 

Ethyl nitrite, C 2 H 5 -N0 2 , is usually prepared by slowly 
dropping concentrated nitric acid (3 c.c.) into a cold mixture 
of alcohol (20 c.c.) and concentrated sulphuric acid (2 c.c.), 
then adding copper turnings (about 4 grams), and distilling 
carefully from a water-bath. 

The distillate consists of a mixture of ethyl nitrite, alcohol, 
and its oxidation products : when mixed with alcohol, it is 
employed in medicine as 'sweet spirit of nitre.' In order to 
prepare pure ethyl nitrite, a mixture of alcohol and dilute sul- 
phuric acid is added to a solution of potassium nitrite ; the 
product is separated, dried over calcium chloride, and distilled. 

Ethyl nitrite is a colourless liquid of sp. gr. 0-947 at 15-5; 



* As 4 O 6 + 4HNO 3 + 4H 2 O = 4H 3 AsO 4 

f 2Cu + 6HN0 3 =2Cu(N0 3 ) 2 +2H 2 + 2HNO,,. 



184 ETHEREAL SALTS OR ESTERS. 

it boils at 17, and has a pleasant, fruity odour like that of 
apples ; it is insoluble in water, and is readily hydrolysed by 
boiling water or dilute alkalies, 

C 2 H 5 -N0 2 + KOH = C 2 H 5 .OH + KN0 2 . 

Methyl nitrite, CH 3 'N0 2 , is a gas ; the higher homologues 
resemble ethyl nitrite. Amyl nitrite, C 5 H n -]S"0 2 , for example, 
prepared by distilling commercial amyl alcohol (p. 106) with 
nitric acid, is a liquid boiling at 96 ; it is used in medicine 
in cases of Angina Pectoris. 

Nitre-paraffins. When ethyl iodide is heated with silver nitrite 
very interesting changes occur : part of the ethyl iodide interacts 
with the silver nitrite, yielding ethyl nitrite, the rest being con- 
verted into nitro-ethane) both changes being expressed by the 
equation, 

C 2 H 5 I + AgNO 2 = C 2 H 5 -NO 2 + Agl. 

Ethyl nitrite and nitro-ethane are isomeric ; the former is simply 
a salt of nitrous acid, HO-N:O, and has the constitution 
C 2 H 5 -0-N:0, whereas the latter probably contains pentavalent 



nitrogen, and has the constitution C 2 H 5 -NQ. 

Compounds, similar to nitro-ethane in constitution and isomeric 
with the corresponding nitrites, may be obtained from other 
halogen ethereal salts in the above manner ; they were discovered 
by V. Meyer, and are termed nitro-paraffins, because they are 
derived from the paraffins by the substitution of the nitro-group 

^ ^ O1 one a ^ om f hydrogen. 



The nitro- paraffins are colourless, pleasant-smelling-liquids, and 
distil without decomposing, but their boiling-points are much 
higher than those of the corresponding nitrites ; nitro-ethane, for 
example, boils at 114, ethyl nitrite at 17. They differ from the 
nitrites in certain important particulars: the nitre-paraffins may 
dissolve in, but are not decomposed by, caustic alkalies, whereas 
the nitrites, like all other ethereal salts, undergo hydrolysis, yield- 
ing an alcohol and a nitrite. The nitre-paraffins are converted into 
amines on reduction, 

C 2 H 5 .N0 2 + 6H = C 2 H 5 -NH 2 + 2H 2 O, 

whilst the nitrites yield hydroxylamine (p. 183) or ammonia, and 
an alcohol, 



ETHEREAL SALTS OR ESTERS. 185 

Ethereal Salts of Sulphuric Acid. 

Dibasic acids, such as sulphuric acid, form two classes of 
salts with alcohols namely, alkyl-hydrogen salts, correspond- 
ing with the metal hydrogen sulphates, and normal alkyl salts, 
corresponding with the normal metallic sulphates, 

Ethyl hydrogen sulphate, C2 ^ 5 >S0 4 Ethyl sulphate (C 2 H 5 ) 2 S0 4 . 

TT 

Potassium hydrogen sulphate, Tr^>SO 4 Potassium sulphate, K 2 SO 4 . 

Ethyl hydrogen sulphate, ethylsiilphuric acid, or sulpho- 
vinic acid (from sulphuric acid and spirit of wine), 
C 2 H 5 -HS0 4 , is formed when ethylene is passed into fuming 
sulphuric acid, or heated with ordinary sulphuric acid, 

C 2 H 4 + H 2 S0 4 = C 2 H 5 -HS0 4 . 

It is prepared by heating alcohol with concentrated sulphuric 
acid, 

C 2 H 5 .OH + H 2 S0 4 = C 2 H 5 .HS0 4 + H 2 0. 

A mixture of equal volumes of alcohol and concentrated sul- 
phuric acid is heated at 100 for about an hour, when part of the 
alcohol is converted into ethyl hydrogen sulphate. The solution is 
then cooled, diluted with water, and treated with a slight excess of 
barium carbonate, when barium sulphate and barium ethylsulphate 
are formed, 

2C 2 H 5 .HS0 4 + BaC0 3 = (C 2 H 5 -SO 4 ) 2 Ba + C0 2 + H 2 0. 

After filtering from the barium sulphate and excess of barium 
carbonate, the cold solution of barium ethylsulphate is treated 
with dilute sulphuric acid as long as a precipitate is produced, and 
filtered again to separate the barium sulphate, 



The filtrate is now free from sulphuric acid; it is evaporated at 
ordinary temperatures under reduced pressure over sulphuric acid, 
when alcohol and water pass off and are absorbed by the sulphuric 
acid, and ethyl hydrogen sulphate remains as a thick, sour liquid. 

Ethyl hydrogen sulphate has an acid reaction, decomposes 
carbonates, and is, in fact, like potassium hydrogen sulphate, 
a monobasic acid, since it contains one atom of hydrogen dis- 



186 ETHEREAL SALTS OB ESTERS. 

placeable by metals. The potassium salt, C 2 H 3 -KS0 4 , may 
be prepared by neutralising the acid with potassium car- 
bonate, or by treating a solution of the barium salt with 
potassium carbonate, and, after filtering, evaporating to dry- 
ness ; it is a colourless, crystalline, neutral compound, readily 
soluble in water. The barium salt, (C 2 H 5 -S0 4 ) 2 Ba, is also 
readily soluble in water, so that ethylsulphuric acid does not 
give a precipitate with barium chloride. 

Ethyl hydrogen sulphate is a very interesting substance, 
as it is an intermediate product in the conversion of alcohol 
into ethylene and ether, and of ethylene into alcohol. When 
boiled with water it yields alcohol, so that it cannot be 
obtained from its aqueous solution by evaporating at 100, 

C 2 H 5 .HS0 4 + H 2 = C 2 H 5 -OH + H 2 S0 4 ; 
when heated with alcohol it gives ether, 

C 2 H 5 -HS0 4 + C 2 H 5 .OH = (C 2 H 5 ) 2 + H 2 S0 4 ; 

and when heated alone, or with concentrated sulphuric acid, 
it yields ethylene, 

C 2 H 5 -HS0 4 = C 2 H 4 + H 2 S0 4 . 

Other alcohols combine with sulphuric acid, yielding alkyl 
hydrogen sulphates corresponding with ethyl hydrogen sulphate ; 
these compounds closely resemble ethyl hydrogen sulphate in 
properties, undergo similar decompositions, and are frequently used 
in preparing other substances. 

Ethyl sulphate, (C 2 H 5 ) 2 SO 4 , the normal or neutral salt, is of 
comparatively little importance ; it may be prepared by warming 
silver sulphate with ethyl iodide, when double decomposition takes 
place, just as when silver sulphate is treated with potassium iodide, 

Ag 2 SO 4 + 2C 2 H 5 I = (C 2 H 5 ) 2 SO 4 + 2AgI. 
It is a colourless liquid, and boils at 208, decomposing slightly. 

MERCAPTANS AND SULPHIDES. 

There are two classes of organic compounds derived from 
hydrogen sulphide namely, the hydrosulphides and the 
sulphides ; the former bear the same relation to the metallic 
hydrosulphides as the alcohols to the metallic hydroxides, 



ETHEREAL SALTS Oft ESTERS. 187 

whereas the latter are related to the metallic sulphides just 
as the ethers to the metallic oxides, 

f Ethyl hydrosulphide, C 2 H 5 -SH /Ethyl sulphide, (C 2 H 5 ) 2 S 

\ Potassium hydrosulphide, K-SH \Potassium sulphide, K 2 S 

f Ethyl hydroxide, C 2 H 5 -OHJ Ethyl oxide, (C 2 H 5 ) 2 O 

\Potassium hydroxide, K- OH \Potassium oxide, K 2 

The organic hydrosulphides or sulphhydrates are usually 
called mercaptans (mercurium captans) on account of their 
property of combining readily with mercuric oxide, forming 
crystalline compounds ; they may be regarded as sulphur- or 
thio-alcohols, and the organic sulphides, as ttiio-etJiers. 

Ethyl mercaptan, C 2 H 5 -SH, may be obtained by treating 
alcohol with phosphorus pentasulphide, 

5C 2 H 5 -OH + P 2 S 5 = 5C 2 H 5 .SH + P 2 5 ; 

it is prepared by distilling a concentrated solution of ethyl 
potassium sulphate with potassium hydrosulphide, 

C 2 H 5 .KS0 4 + KSH = C 2 H 5 .SH + K 2 S0 4 , 
or by the interaction of ethyl chloride and potassium hydro- 
sulphide. It is a colourless liquid, has a most offensive smell, 
and boils at 36. The hydrogen atom in the HS- group is 
displaceable by metals more readily than that in the HO- 
group of the alcohols ; when ethyl mercaptan is treated with 
sodium or potassium, it yields sodium or potassium mercap- 
tide, C 2 H 5 -SNa, or C 2 H 5 -SK, with evolution of hydrogen; 
when shaken with mercuric oxide it yields mercuric mer- 
captide, 

2C 2 H 5 -SH + HgO = (C 2 H 5 -S) 2 Hg + H 2 O, 

a crystalline compound, which is decomposed by hydrogen 
sulphide, giving ethyl mercaptan, 

(C 2 H 5 -S) 2 Hg + SH 2 = 2C 2 H 5 -SH + HgS. 

Other mercaptans can be obtained by similar reactions ; they are 
characterised by having a highly unpleasant, garlic-like smell, and 
in chemical properties they resemble ethyl mercaptan ; on oxidation 
with nitric acid they are converted into sulphonic acids, 
C 2 H 5 -SH + 3O = C 2 H 5 .SO 2 -OH. 

Bthylsul phonic Acid. 



188 ETHEREAL SALTS OR ESTERS. 

Sulphonic acids contain the group SO.,-OH, the alkyl group 
being attached to the sulphur atom ; they are powerful acids, 
forming salts, such as potassium ethylsulphonate, C 2 H 5 -S0 2 'OK. 
They differ from the alkyl hydrogen sulphites (with which they 
are isomeric) in not being hydrolysed when boiled with dilute 
aqueous potash. They stand, therefore, in much the same relation- 
ship to the alkyl hydrogen sulphites as the nitre-paraffins to the 
nitrites (p. 184). 

Ethyl sulphide, (C 2 H 5 ) 2 S, may be obtained by heating 
ether with phosphorus pentasulphide, 

5(C 2 H 5 ) 2 + P 2 S 5 = 5(C 2 H 5 ) 2 S + P 2 5 , 

and by distilling a concentrated aqueous solution of ethyl 
potassium sulphate with potassium sulphide, 

2C 2 H 5 .KS0 4 + K 2 S - (C 2 H 5 ) 2 S + 2K 2 S0 4 . 
It is a colourless, neutral, unpleasant-smelling liquid, and 
boils at 91; like the ethers, it does not contain hydrogen 
displaceable by metals, and is a comparatively inert substance. 

Other sulphides can be obtained by similar methods, and have 
similar properties ; on oxidation with nitric acid they are finally 
converted into very stable crystalline compounds termed sulphones, 
of which ethyl sulphone, (C 2 H 5 ) 2 S0 2 , is an example. 

Sulphonal, (CH 3 )2C(S0 2 'C 2 H 5 ) 2 , is an important and interesting 
compound, first prepared by Baumann, arid largely used as a 
soporific. Although acetone and other ketones do not interact 
readily with alcohols giving acetals, as aldehydes do (p. 143), 
they condense with mercaptans in presence of hydrogen chloride ; 
acetone and ethyl mercaptan, for example, give acetone mercaptole 
(b. p. 190-191), 

(CH 3 ) 2 CO + 2C 2 H 5 .SH = (CH 3 ) 2 C(S.C 2 H 5 ) 2 + H 2 O. 
When this mercaptole is oxidised with potassium permanganate, it 
unites directly with four atoms of oxygen (the divalent sulphur 
atom becoming tetra- or hexavalent), giving sulphonal, a crystalline 
compound melting at 126. 

Esters or Ethereal Salts of Organic Acids. 

Ethyl acetate, C 2 H 3 2 -C 2 H 5 , or CH 3 -CO-OC 2 H 5 , is formed 
when acetyl chloride or acetic anhydride is treated with 
alcohol, 



ETHEREAL SALTS OR ESTER8. 189 

CHg-COCl + C 2 H 5 :OH - CH 3 .COOC,H 6 4- HC1 
(CH 3 -CO) 2 + C 2 H 5 -OH = CH 3 .COOC 2 H 5 + CH 3 .COOH ; 

also when a metallic salt of acetic acid is heated with a 
halogen salt of ethyl alcohol, 

CH 3 .COOAg + C 2 H 6 Br - CH 3 -COOC 2 H 5 + AgBr, 
and when alcohol is heated with glacial acetic acid, 

CH 3 .COOH + C 2 H 5 .OH = CH 3 .COOC 2 H 5 + H 2 0. 

It is prepared by gradually adding a mixture of equal volumes of 
alcohol and acetic acid to a mixture of equal volumes of alcohol 
and concentrated sulphuric acid, heated at about 140 in a retort 
connected with a condenser ; this process, like that by which ether 
is prepared, is theoretically continuous, the alcohol and sulphuric 
acid combining to form ethyl hydrogen sulphate, which then inter- 
acts with acetic acid, forming ethyl acetate and sulphuric acid, 



The distillate is shaken with a concentrated solution of sodium 
chloride containing some sodium carbonate, when the alcohol and 
acetic acid dissolve, the ethyl acetate separating as an oil ; it is 
dried over anhydrous calcium chloride, and purified by fractional 
distillation. 

Ethyl acetate is a colourless, mobile liquid, having a pleasant, 
fruity odour, and boiling at 77 ; it is specifically lighter than 
water, in which it is moderately easily soluble. It is readily 
hydrolysed by hot alkalies, more slowly by hot mineral 
acids, and by water, 

CH 3 -COOC 2 H 5 + H 2 = CH 3 .COOH + C 2 H 5 -OH. 
When treated with concentrated ammonia it yields acetamide 
and alcohol, 

CH 3 -COOC 2 H 5 + NH 3 = CH 8 .CO.NH 2 + C 2 H 5 -OH. 

Since ethyl acetate has a rather characteristic smell, and is 
formed when acetic acid or any of its salts is warmed with 
alcohol and concentrated sulphuric acid, the presence of acetic 
acid or an acetate may be readily detected by this reaction, 
the so-called < acetic-ether ' test. 

In hydrolysing most ethereal salts, and in many other operations, 



190 



ETHEREAL SALTS OR ESTERS. 



as, for example, in the hydrolysis of acetyl derivatives (p. 162) and 
in the synthesis of alkyl derivatives of ethyl acetoacetate (p. 196) 

it is often necessary to boil the 
aqueous, alcoholic, ethereal, or other 
solution for a long time ; in order, 
therefore, to avoid loss of solvent, 
or of the substances present in solu- 
tion, the flask or other vessel is 
connected with a reflux condenser 
(fig. 21), so that the vapours, which 
would otherwise pass away, are con- 
densed, the liquid running back into 
the flask. The latter may be heated 
over a piece of wire-gauze or on a 
sand-bath ; but when alcohol, ether, 
or other substances of low-boiling 
point are being used, a water-bath 
is always employed. With appara- 
tus similar to that shown, a liquid 
may be kept constantly boiling 
for days without requiring any 
attention. 

SUMMARY AND EXTENSION. 

Although the esters of mineral 
acids are, on the whole, very similar 
in chemical properties, they are 
derived from acids of such diverse 
characters that slight differences in 
behaviour are only to be expected. 
The esters of organic acids, on the 
other hand, being derived from acids 
of similar nature, resemble one 

another in chemical properties so very closely that they may 

be described in a general manner. 
The esters of organic acids may all be produced by treating an 

alcohol with the chloride or anhydride of the acid, 

C 3 H r COCl + CH 3 .OH = C 3 H 7 .COOCH 3 + HC1, 

and by heating a metallic salt of the acid with a halogen salt of an 
alcohol, 

C 3 H 5 .COOAg + CH 3 I = C 2 H 5 .COOCH 3 + Agl. 

Esters in general are formed when an alcohol is mixed with an 







21 - 



ETHEREAL SALTS OR ESTERS. 191 

acid, but the change, which is a gradual one, is never complete, 
because, after the interaction has proceeded for some time, the 
quantity of ester decomposed by the water produced is equal to 
that formed by the combination of the acid with the alcohol ; in 
other words, a condition of equilibrium is established when the two 
changes represented by the equations, 

CH 3 .OH + C 2 H 4 O 2 = C 2 H 3 2 .CH 3 + H 2 O 
C 2 H 3 2 .CH 3 + H 2 = CH 3 .OH + C 2 H 4 O 2 

balance one another; this is usually expressed by writing the 
equation thus, 

CH 3 .OH + C 2 H 4 2 Z C 2 H 3 O 2 .CH 3 + H 2 O, 

to indicate that the change takes place in either direction. 

The proportion of alcohol converted into ester depends on the 
nature of the alcohol and of the acid, and on their relative 
quantities ; it is independent of the temperature, but the higher 
the temperature the sooner the condition of equilibrium is attained. 
These facts were established by Berthelot and by Menschutkin, 
who carefully studied the conditions under which ' esterification ' 
takes place. 

Now, if the water produced during esterification be prevented in 
some way from decomposing the ester, the desired change should 
take place far more completely, and the whole of the acid and of 
the alcohol, if present in molecular proportions, might possibly be 
converted into ester. These considerations led to the use of 
' dehydrating agents ' in the preparation of esters, substances such 
as zinc chloride, hydrogen chloride, or sulphuric acid being added 
to the mixture of alcohol and acid to ' bind ' the water and prevent 
it from decomposing the ester. In practice, the results of doing 
this are very satisfactory, and at the present time the two methods 
usually employed in preparing esters of organic acids are (a) by 
passing dry hydrogen chloride into a boiling mixture of the acid 
and alcohol contained in a flask provided with a reflux condenser ; 
(&) by warming a mixture of the acid and alcohol with concentrated 
sulphuric acid. The action of the mineral acids in the process of 
esterification is, however, by no means so simple as it was at first 
thought to be, and is not yet thoroughly understood ; * in the case 
of sulphuric acid, an alkyl hydrogen sulphate is doubtless formed 
as an intermediate product (compare p. 189). The isolation of the 
ethereal salt is sometimes accomplished by distillation, as in the 
case of ethyl acetate ; as a rule, however, when esterification is at 

* An explanation based on the ionic dissociation hypothesis has been 
recently advanced. 



192 ETHEREAL SALTS OR ESTERS. 

an end the solution is poured into water and the ethereal salt 
isolated by filtration (if a solid) or by extraction with ether (if a 
liquid, or if it be soluble in water). 

When only a small quantity of acid is at disposal, and it is 
desired to prepare one of its esters, it is converted into the silver 
salt, and the latter is warmed with a halogen ethereal salt, such 
as methyl iodide. 

Esters are usually colourless, neutral, pleasant-smelling liquids, 
sparingly soluble or insoluble in water ; they distil unchanged under 
atmospheric pressure, and are volatile in steam, but a few, such 
as cetyl palmitatej C 16 H 31 O2'C 16 H33, which occurs in spermaceti, 
are solid at ordinary temperatures, and decompose when heated. 
They are all comparatively inert substances, and resemble the 
ethers perhaps more closely than any other class of compounds, 
although, at the same time, they differ from them in several 
important respects. The hydrogen ethereal salts are usually 
non-volatile, and act like acids. 

All esters are decomposed by aqueous mineral acids and alkalies 
(sometimes even by water), the change which they undergo being 
spoken of as hydrolysis (or saponification, p. 172), 



+ Ba(OH) 2 =(H.COO) 2 Ba + 2CH 3 .OH. 

The rapidity with which hydrolysis takes place depends on the 
temperature and concentration of the solution, as well as on 
the nature of the ester and of the hydrolysing agent ; as a rule, 
potash, soda, and barium hydroxide are the most powerful 
hydrolysing agents. Since, however, esters are generally in- 
soluble in water, if they be boiled with aqueous alkalies or 
mineral acids they are not attacked very quickly ; it is usual, 
therefore, to employ alcoholic potash, &c., in which the esters 
are soluble. 

The identification of esters, as such, is usually impossible because 
they are generally liquids and the only means at disposal is a 
determination of the boiling-point; it is necessary, therefore, to 
first hydrolyse with boiling aqueous potash, and then to separate 
and identify the alcohol and acid which have been produced. 

All esters of organic acids yield amides on treatment with 
concentrated aqueous or alcoholic ammonia, 



whereas the halogen ethereal salts give amines with alcoholic 
ammonia (p. 205), 

= C 2 H 5 .NH 8 , HI. 



SYNTHESIS OF KETONES AXD FATTY ACIDS. 193 

The esters of organic acids afford excellent examples of isomerism ; 
ethyl formate, H'CO'O'CH 2 -CH 3 , for example, is isomeric with 
methyl acetate, CH 3 .CO-0-CH 3 ; propyl formate, H-COOC 3 H 7 , 
is isomeric with ethyl acetate, CH 3 -COOC 2 H 5 , and with methyl 
propionate, C 2 H 5 -COOCH 3 , and so on. 

Many esters occur in the fruit, flower, and other parts of 
plants, and it is to their presence in many cases that the scent 
of the part is due ; many are prepared artificially for flavouring 
sweets, pastry, perfumes, &c. ; amyl acetate, CH 3 -COOC 5 H n , for 
example, prepared from commercial amyl alcohol, has a strong 
smell of pears, and is known as ' pear-oil ; ' methyl butyrate, 
C 3 H 7 -COOCH 3 , is sold as 'pine-apple oil,' and isoamyl isovalerate 
as 'apple-oil.' 



CHAPTER XL 

SYNTHESIS OF KETONES AND FATTY ACIDS WITH THE AID 
OF ETHYL ACETOACETATE AND ETHYL MALONATE. 

In the whole domain of organic chemistry probably no 
compounds have been more extensively used for synthetical 
purposes than ethyl acetoacetate and ethyl malonate, and 
certainly one of the most important uses to which these sub- 
stances have been put is the synthesis of a great number of 
ketones and fatty acids, many of which could have been 
prepared only with great difficulty by other methods. 

Ethyl acetoacetate, CH 8 .CO-CH 2 .COOEt* the ethyl ester 
of acetoacetic acid, is formed when ethyl acetate is digested 
with sodium, and the product decomposed with dilute acids. 
The final result is that 2 molecules of ethyl acetate combine 
with loss of 1 molecule of alcohol, the following equation 
representing the reaction in its simplest form (compare 
p. 199), 

CH 3 . COj6C 2 H 5 + H!CH 2 .COOC 2 H 5 = CH 3 -CO.CH 2 .COOC 2 H 5 
+ C 2 H 5 .OH. 

* Et is used to represent C 2 H 5 - in this and in many of the following 
formulae for the sake of clearness. 

M 



194 SYNTHESIS OF KETONES AND FATTY ACIDS. 

Sodium (30 grams), in the form of fine wire or shavings, is 
added to dry ethyl acetate (300 grams) contained in a flask 
connected with a reflux condenser. As soon as the vigorous 
action which sets in has subsided, the flask is heated on a water- 
bath, until bright particles of sodium are no longer visible on 
shaking. 

The thick brownish semi-solid product, which consists of the 
sodium derivative of ethyl acetoacetate (and of sodium ethoxide), 
is allowed to cool, and then treated with dilute (1 = 4) hydrochloric 
acid, until the solution is distinctly acid to test-paper. An equal 
volume of a saturated solution of salt is now added, and the oily 
layer separated from the aqueous solution, dried over anhydrous 
calcium chloride, and fractionated. At first a quantity of un- 
changed ethyl acetate passes over ; the thermometer then rises 
rapidly to about 160, the fraction 175-185 consisting of nearly 
pure ethyl acetoacetate, and weighing 40-50 grams, being collected 
separately. 

Ethyl acetoacetate is a colourless liquid, boiling at 181, 
and having an agreeable, fruity odour ; it is sparingly soluble 
in water, but readily in alcohol and ether. The alcoholic 
solution assumes a beautiful violet colour on the addition 
of ferric chloride. 

It is remarkable that, although neutral to test-paper, ethyl 
acetoacetate possesses some properties of an acid ; it dissolves 
in dilute potash or soda, and is reprecipitated on the addition 
of acids, but it is insoluble in alkali carbonates. 

These properties are due to the fact that it contains a 
hydrogen atom displaceable by certain metals under certain 
conditions. 

The sodium derivative, CHg-CO-CHNa-COOEt, which 
is so much used in synthetical processes, may be prepared 
by adding sodium to a solution of ethyl acetoacetate in ether 
or benzene and then boiling for several hours, 
2CH 8 ,CO.CH 2 .COOEt + 2Na = 2CH 3 .CO.CHNa.COOEt + H 2 ; 

the metal gradually dissolves, and the sodium derivative 
separates as a colourless (or yellowish) crystalline mass, which 
is readily soluble in water and alcohol ; it rapidly deliquesces 
in contact with moist air, and undergoes decomposition 



SYNTHESIS OF KETONES AND FATTY ACIDS. 195 

when its aqueous solution is boiled. A solution of the 
sodium derivative is easily obtained by mixing ethyl aceto- 
acetate with a cold alcoholic solution of sodium ethoxide, 
dL-CO-CEL-COOEt + NaO-C 9 H, - 



CH 3 .CO-CHNa.COOEt + C 2 H 5 -OH. 

When shaken with a saturated solution of copper acetate, 
ethyl acetoacetate forms a green crystalline copper derivative, 
(C 6 H 9 3 ) 2 Cu. 

This property of forming metallic derivatives is due to the 
presence of the group -CO-CH 2 -CO- ; all substances which 
contain this, or the group -CO-CH-CO-, yield derivatives 

with sodium, frequently also with other metals. 

The sodium derivative of ethyl acetoacetate interacts readily 
with alkyl halogen compounds with formation of a sodium 
halogen salt and a mono-substitution derivative of ethyl aceto- 
acetate, the alkyl group taking the place previously occupied 
by the metal. Thus methyl iodide interacts with the sodium 
derivative of ethyl acetoacetate, forming ethyl methylacGto- 
acetate, 

CH 3 .CO.CmsTa.COOC 2 H 5 + Mel * = 

CH 3 .CO.CHMe-COOC 2 H 5 + Nal, 

whereas when propyl bromide is employed, ethyl propyl- 
acetoacetate, CHg-CO-CHPr-COOCaHs, results, and so on. 

All the alkyl wzowo-substitution derivatives of ethyl aceto- 
acetate contain the group -CO-CH-CO, and are therefore 

l 
capable of forming sodium derivatives such as 

CH 3 .CO.CNaMe-COOC 2 H 5 , CH 3 .CO.C^aPr.COOC 2 H 5 , 

&c., on treatment with sodium or sodium ethoxide, the metal 
taking the place of the hydrogen atom in the -CH- group. 

From these sodium derivatives, by the action of alkyl 
halogen compounds, di-substitution derivatives of ethyl aceto- 
acetate are produced thus, 

* The symbols Me, &c., are used here for the sake of clearness. 



196 SYNTHESIS OF KETONES AND FATTY ACIDS. 

CH 3 .CO.CNaMe.COOC 2 H 5 + EtBr = 

CH 3 .CO-CEtMe.COOC 2 H 5 + NaBr. 

Ethyl Ethylmethylaceioacetate. 

CH 3 .CO.CNaPr-COOC 2 H 5 + PrI = 

CH 3 .CO-CPrPr.COOC 2 H 5 + Nal. 

Ethyl Dipropylacetoacet&te. 

In order, then, to obtain a di-substituted ethyl acetoacetate, 
the mono-substitution derivative is first prepared and then 
treated with sodium ethoxide and the alkyl halogen com- 
pound; the introduction of both alkyl groups cannot be 
carried out in one operation, because ethyl acetoacetate 
does not form a disodium derivative of the constitution 
CH 3 .CO.CI*a 2 .COOC 2 H 5 . 

The synthesis of the alkyl substitution products of ethyl aceto- 
acetate is usually carried out as follows : The theoretical quantity 
of sodium (1 atom) is dissolved in 10-12 times its weight of absolute 
alcohol, and the solution of sodium ethoxide is thoroughly cooled. 
The ethyl acetoacetate, or the mono -substituted ethyl acetoacetate 
(1 mol.), and a slight excess of the alkyl halogen compound (1 mol.), 
are now gradually added, the whole being well cooled during the 
operation ; the flask is then connected with a reflux condenser, 
and carefully heated on a water-bath until neutral to litmus- 
paper. In order to isolate the product, the alcohol is distilled from 
a water-bath, the residue mixed with water to dissolve the pre- 
cipitated sodium salt, and the whole extracted with ether ; the 
ethereal solution is washed with water, dried with anhydrous 
calcium chloride, the ether distilled off, and the residual oil purified 
by fractional distillation. 

The following are some of the more important mono- and di-sub- 
stitution products of ethyl acetoacetate, with their boiling-points : 

B.i. 

Ethyl we%Jacetoacetate, CH 3 -CO-CHMe-COOC 2 H 5 187 

Ethyl dimethyla,cetoa,ceta,te, CH 3 -CO-CMe2-COOC 2 H 5 184 

Ethyl e%Zacetoacetate, CH 3 -CO-CHEt-COOC 2 H 5 198 

Ethyl cfte%Jacetoacetate, CH 3 COCEt2-COOC 2 H 5 218 

Ethyl />r0p^acetoacetate, CH 3 -CO CHPr*-COOC 2 H 5 209 

Ethyl wo^rop^acetoacetate, CH 3 .CO-CHpr/3.COOC 2 H 5 201 

The mono-substituted ethyl acetoacetates resemble ethyl aceto- 
acetate in chemical behaviour and give a characteristic bluish- 



SYNTHESIS OP KETONES AND PATTY ACIDS. 197 

violet colouration with ferric chloride. The ^'-substituted ethyl 
acetoacetates, however, do not contain a hydrogen atom displaceable 
by metals, and do not give the violet ferric chloride reaction. 

One of the most important changes which ethyl aceto- 
acetate and its derivatives undergo is that which takes place 
when they are treated with alkalies or mineral acids. 
Alkalies at ordinary temperatures simply hydrolyse the esters 
with formation of the alkali salts of the corresponding acids, 
CH 3 .CO-CH 2 .COOEt i- KOH = CH 3 .CO.CH 2 -COOK + Et-OH. 

Potassium Acetoacetate. 

On acidifying the solution and extracting with ether, the free 
acids are obtained ; these /3-ketonic acids,* however, are very 
unstable, decomposing in many cases at ordinary temperatures, 
and always very readily on warming, yielding carbon dioxide 
and a ketone, 

CH 3 .CO.CH 2 -COOH = CH 3 .CO.CH 3 + C0 2 
CH 3 .CO.CEt 2 .COOH = CH 3 .CO-CHEt 2 + C0 2 . 
When heated with alkalies, ethyl acetoacetate and its deriva- 
tives are decomposed in two ways, the course of the decom- 
position depending to a great extent on the nature and 
concentration of the alkali used. 

Boiling dilute alcoholic potash converts these substances 
into ketones, with separation of potassium carbonate (ketonic 
hydrolysis), 

CHg-CO-CHajCOOEt + 2KOH = CH 3 -CO.CH 3 + K 2 C0 3 

+ Et-OH 

CH 3 .CO.CEt 2 |COOEt + 2KOH = CH 3 -CO.CHEt 2 + K 2 C0 8 
+ Et-OH. 

Ketonic hydrolysis is also brought about by boiling with 
dilute mineral acids. If, however, strong alcoholic potash be 
employed, the decomposition takes place in quite a different 
manner, the potassium salt of a fatty acid being the principal 
product (acid hydrolysis), 

* The ketonic oxygen atom is here combined with the /3-carbon atom 
(compare p. 166). 



198 SYNTHESIS OF KETONES AND FATTY ACIDS. 

CH 3 .COiCH 2 .COOEt + 2KOH = 2CH 3 -COOK + Et-OH 

CH 3 .CO;CEt 2 -COOC 2 H 5 + 2KOH = CH 3 -COOK 
+ Et 2 CH.COOK + C 2 H 5 -OH. 

Potassium Diethylacetate. 

Ethyl acetoacetate is, therefore, a very important com- 
pound, as with its aid any fatty acid, or any ketone (con- 
taining the group CH 3 -CO-), can be synthetically prepared, 
provided the requisite alkyl halogen compound can be 
obtained. 

Example. If an acid of the constitution (C 2 H 5 )(C 3 H 7 )CH-COOH 
namely, ethylpropylacetic acid be required, ethyl ethyl&vztQ- 
acetate, CH 3 .CO-CH(C 2 H 5 ).COOC 2 H 5 , might be first prepared; on 
treating the sodium derivative of this substance with propyl iodide, 
ethyl e%/pro^acetoacetate, CH 3 .CO.C(C 2 H 5 )(C 3 H 7 ).COOC 2 H 5 , 
would be formed, and the latter, when heated with strong alcoholic 
potash, would yield the potassium salt of the acid required, 
CH 3 .CO.C(C 2 H 5 )(C 3 H 7 )-COOC 2 H 5 + 2KOH = 

CH 3 -COOK + CH(C 2 H 5 )(C 3 H 7 ).COOK + C 2 H 5 -OH. 

Example. If a ketone of the constitution CH 3 -CO-CH 2 -C 4 H 9 
namely, butyl acetone be required, ethyl butylacetoacetate, 
CH 3 .CO.CH(C 4 H 9 ).COOC 2 H 5 , would be prepared by treating the 
sodium compound of ethyl acetoacetate with butyl iodide, and 
then decomposed by boiling with dilute alcoholic potash or dilute 
sulphuric acid, 
CH 3 .CO.CH(C 4 H 9 ).COOC 2 H 5 



The acid and the ketonic hydrolysis of ethyl acetoacetate and 
its derivatives always take place to some extent simultaneously, 
whether weak or strong alkali be used. It is not possible, for 
instance, to decompose an ethyl acetoacetate derivative with 
strong alkali without a small amount of ketone being formed, and 
when dilute alkali is used, a certain quantity of the salt of a fatty 
acid is invariably produced ; nevertheless the relative quantities of 
the products depend very largely on the strength of the alkali 
employed. 

Constitution of Ethyl Acetoacetate. On hydrolysis with 
cold alkalies, ethyl acetoacetate is converted into a salt of 



SYNTHESIS OF KETONES AND FATTY ACIDS. 199 

acetoacetic acid, and when this acid is gently warmed it is 
decomposed into acetone and carbon dioxide ; it may be 
assumed, therefore, that acetoacetic acid has the constitution 
CH 3 -CO-CH 2 -COOH, and its ester, ethyl acetoacetate, may be 
represented by the formula CH 3 .CO-CH 2 -COOC 2 H 5 . 

That ethyl acetoacetate contains a ketonic group -CO- 
seems to be proved by many facts ; it interacts with 
hydroxylamine and phenylhydrazine, combines with sodium 
bisulphite and hydrogen cyanide, and on reduction it is con- 
verted into /3-hydroxybutyric acid, CH 3 .CH(OH).CH 2 -COOH, 
or its ethyl salt. In many of its reactions, however, 
ethyl acetoacetate behaves as if it contained a hydroxyl- 
group, and had the constitution represented by the formula 
CH 3 .C(OH):CH.COOC 2 H 5 . These facts have led to the 
conclusion that ethyl acetoacetate may exist in two different 
forms which are easily converted into one another. 

Ever since the discovery of ethyl acetoacetate by Geuther in 1863 
chemists have been trying to explain its formation from ethyl 
acetate, and to decide between the two possible formulae (given 
above) by which its constitution must be represented. The fact 
that ethyl acetoacetate contains a hydrogen atom displaceable by 
sodium, whilst ethyl acetate does not, s'eems to show that the 
former, like ethyl alcohol, contains a hydroxyl-gmup, a view which 
is confirmed by the knowledge that in the vast majority of organic 
compounds hydrogen directly united with carbon is not displace- 
able by metals. At first sight it might seem absurd to represent 
the sodium derivative by the formula CH 3 .C(ONa):CH.COOEt, 
because when this compound interacts with alkyl halogen com- 
pounds the alkyl-group does not become united to oxygen but to 
carbon; this might be explained, however, by assuming that the 
first change consisted in a direct addition of the alkyl halogen 
compound to the unsaturated sodium derivative, giving an unstable 
product which immediately underwent decomposition, 
CH 3 .C(ONa):CH.COOEt + MeI = CH 3 .CI(ONa).CMeH.COOEt, 
CH 3 .CI(ONa).CMeH.COOEt-CH 3 .CO.CMeH.COOEt + NaI. 

A similar assumption, namely, the formation of an unstable inter- 
mediate product, may also be made to explain the action of sodium 
on ethyl acetate (Claisen) ; in the first place sodium ethoxide is 
probably produced by the action of the metal on traces of alcohol 



200 SYNTHESIS OF RETONES AND FATTY ACIDS. 

contained in, or formed from, the ester ; combination then ensues 
between the sodium ethoxide and the ethyl acetate (which strictly 
speaking is an unsaturated compound), giving an unstable deriva- 
tive of ortho-acetic acid, CH 3 C(OH) 3 , 

CH 3 .COOEt + NaOEt = CH 3 .C(OEt) 2 .ONa ; 

this additive product then condenses with ethyl acetate, giving 
alcohol and the sodium derivative of ethyl acetoacetate (ethyl 
hydroxycrotonate), 
CH 3 .C(OEt) 2 .ONa + CH 3 .COOEt = 

CH 3 .C(ONa):CH.COOEt + 2Et-OH. 

Many substances which, like ethyl acetoacetate, contain the 
group R-CO-CH 2 -, or R.CO-CH<, are easily changed into 
isomeric hydroxy-compounds, R-C(OH) = CH- or R-C(OH) = C<, 
which may be reconverted into the keto-derivatives ; such iso- 
merides differ from isomeric compounds generally, in the readiness 
with which they are changed one into the other by heat or by the 
action of various chemical agents, and are termed tautomeric forms 
or tautomerides. The hydroxy-form is usually known as the 
' enol ' modification, the isomeride being named the ' keto ' form. 
When one of these tautomeric forms is more stable than the other 
under ordinary conditions, the latter is often called the labile modi- 
fication ; but, as a rule, it is difficult to say which is the more 
stable form, as it all depends on the conditions under which the 
tautomerides are placed. 

Other Ketonic Acids. 

Pyruvic acid, or acetylformic acid, CH 3 -CO-COOH, is formed by 
the dry distillation of tartaric acid (p. 247), 



It is an oily, sour-smelling liquid, distils at 165-170, and is 
soluble in water in all proportions. It interacts with hydroxyl- 
amine, and gives with phenylhydrazine in aqueous solution a very 
sparingly soluble phenylhydrazone, CH 3 -C(N 2 HC 6 H 5 ).COOH, the 
formation of which serves as a ready means of detecting the acid, 
even when present in small quantity. When treated with sodium 
amalgam and water, pyruvic acid is reduced to lactic acid (p. 231), 

CH 3 .CO.COOH + 2H = CH 3 .CH(OH).COOH. 

Levulinic acid (/3-acetylpropionic acid), CH 3 .CO-CH 2 -CH 2 .COOH, 
is produced when starch, sucrose, glucose, fructose, and other 



SYNTHESIS OF KETONES AND FATTY ACIDS. 201 

carbohydrates containing 6, or a multiple of 6, carbon atoms are 
boiled with dilute hydrochloric acid. 

It melts at 33-5 and distils at 239; it is very soluble in 
water, interacts readily with hydroxylamine and phenylhydrazine, 
and when reduced with sodium amalgam and water it yields 
7-hydroxyvaleric acid, CH 3 .CH(OH).CH 2 .CH 2 .COOH. Levulinic 
acid is isomeric with methylacetoacetic acid or a-acetylpropionic 
acid, CH 3 .CO.CH(CH 3 ).COOH ; its name is derived from levulose 
(fructose), from which it was first obtained. 

a-Ketonic acids, such as pyruvic acid, and 7-ketonic acids, such 
as levulinic acid, show a behaviour very different from that of 
j8-ketonic acids, such as acetoacetic acid ; they are not decomposed 
when heated moderately strongly, arid their esters do not contain 
hydrogen displaceable by metals. 

Ethyl malonate, CH 2 (COOC 2 H 5 ) 2 , does not belong to the 
same class of substances as ethyl acetoacetate; it is, however, 
conveniently considered in this chapter on account of its 
employment in the synthesis of fatty acids. 

When potassium chloracetate is digested with potassium 
cyanide in aqueous solution, potassium cyanacetate is pro- 
duced, 

CH 2 C1-COOK + KCN = CH 2 (CN)-COOK + KC1. 
This salt, on hydrolysis with hydrochloric acid, yields malonic 
acid (p. 239), 
CH 2 (CN)-COOK + 2HC1 + 2H 2 = 

CH 2 (COOH) 2 + KC1 + NH 4 C1 ; 

but if the dry potassium cyanacetate be mixed with alcohol 
and the mixture saturated with hydrogen chloride, ethyl 
malonate is produced, 
CH 2 (CN)-COOK + 2HC1 + 2C 2 H 5 -OH = 

CH 2 (COOC 2 H 5 ) 2 + KC1 + NH 4 C1. 

Preparation. Chloracetic acid (100 grams) is dissolved in water 
(200 c.c.) and neutralised with potassium carbonate (76 grams); 
potassium cyanide (75-80 grams) is then added, and the whole 
heated in a large porcelain basin until a vigorous reaction 
commences. As soon as this has subsided, the solution is 
evaporated on a sand-bath, the thick semi-solid residue being 
constantly stirred with a thermometer until the temperature 



202 SYNTHESIS OF KETONES AND FATTY ACIDS. 

reaches 135 ; the solid cake of potassium chloride and cyanacetate 
is powdered, transferred to a flask, an equal weight of absolute 
alcohol added, and the boiling mixture saturated with dry hydrogen 
chloride (compare p. 191). When cold, the solution is poured 
into twice or thrice its volume of ice- water ; the product is then 
extracted with ether, the ethereal solution washed with water, 
dried with anhydrous calcium chloride, and the ether distilled oft'. 
The crude oil is purified by fractional distillation ; the portion 
boiling at 195-200, after two or three distillations, consists of 
practically pure ethyl malonate. 

c*o or^ TT 

Ethyl malonate, CH 9 < '~ ** like ethyl acetoacetate, 



contains the group -CO-CH 2 -CO-, and forms a sodium 
derivative when it is treated with the metal or with 
sodium ethoxide, 

2CH 2 (COOC 2 H 5 ) 2 + 2Na = 2CHNa(COOC 2 H 5 ) 2 + H 2 
CH 2 (COOC 2 H 5 ) 2 + C 2 H 5 -NaO = CHNa(COOC 2 H 5 ) 2 + C 2 H 5 - OH. 

Unlike ethyl acetoacetate, it does not dissolve in aqueous 
alkalies, because its alkali derivatives are decomposed by water, 
and it does not give a colouration with ferric chloride. 

The sodium derivative of ethyl malonate interacts readily 
with alkyl halogen compounds, yielding homologues of ethyl 
malonate, 

CHNa(COOC 2 H 5 ) 2 + EtI = CHEt(COOC 2 H 5 ) 2 + ISTal ; 

Ethyl Ethylmalonate. 

these mono-substitution derivatives, like those of ethyl aceto- 

acetate, are again capable of forming sodium derivatives, 

which, by further treatment with alkyl halogen compounds, 

yield di-substitution derivatives of ethyl malonate, 

CHEt(COOC 2 H 5 ) 2 + NaOEt = CNaEt(COOC 2 H 5 ) 2 + Et-OH 

CNaEt(COOC 2 H 5 ) 2 + PrI = CPrEt(COOC 2 H 5 ) 2 + Nal. 

Ethyl Propylethylma.loua.te. 

In this way a great number of derivatives may be obtained, 
the syntheses being carried out exactly as described in the 
case of the substitution products of ethyl acetoacetate. 

Ethyl malonate and its derivatives are hydrolysed by 



SYNTHESIS OP KETONES AND FATTY ACIDS. 203 

boiling alcoholic potash with formation of the potassium 
salts of the corresponding acids, 

CHEt(COOC 2 H 5 ) 2 + 2KOH = CHEt(COOK) 2 + 2C 2 H 5 -OH 

Potassium Ethylmalouate. 

CEtPr(COOC 2 H 5 ) 2 + 2KOH = CEtPr(COOK) 2 + 2C 2 H 5 -OH. 

Potassium E thylpropylmalonate. 

Malonic acid and the dicarboxylic acids derived from it are 
rapidly and quantitatively decomposed at about 200 with 
evolution of carbon dioxide and formation of fatty acids. 
This behaviour is shown by all acids which contain two 
carboxyl-groups directly combined with the same carbon atom 
(p. 240), 

CH 2 (COOH) 2 = CH 3 -COOH + C0 2 
CEtPr(COOH) 2 = CEtPrH-COOH + C0 2 . 

Ethylpropylmalonic Acid. Ethylpropylacetic Acid. 

Ethyl malonate, therefore, is of the utmost service in the 
synthesis of fatty acids, and is, indeed, more used for this 
purpose than ethyl acetoacetate, because in the case of the 
latter, ketones are always formed on hydrolysis as bye- 
products. The value of both synthetical methods is also 
much enhanced by the fact that the constitution of the acid 
(or ketone) obtained is always known, which is very often not 
the case when other methods are employed. 

Example. Normal valeric acid, CH 3 .CH 2 .CH 2 -CH 2 .COOH, is to 
be prepared synthetically. In the first place the sodium derivative of 
ethyl malonate would be heated with propyl iodide, and the resulting 
ethyl propylmalonate, CH 3 .CH 2 .CH 2 .CH(COOC 2 H 5 ) 2 , hydrolysed 
with boiling alcoholic potash. The propylmalonic acid obtained 
from the potassium salt is heated at about 200, or distilled, when 
it decomposes into normal valeric acid and carbon dioxide, 



The examples already given will afford some indication of the 
great usefulness of ethyl acetoacetate and of ethyl malonate in 
synthesising fatty acids and ketones, but there are many other 
synthetical operations in which these important esters are employed. 
Their sodium derivatives interact readily, not only with alkyl 
halogen esters, hut also with acid chlorides, &c., such as acetyl 
chloride, 



204 ALKYL COMPOUNDS OP NITROGEN, PHOSPHORUS, ETC. 

CHg-CO-CHNa-COOEt + CH 3 -COC1 = 

CH 3 .CO.CH(CO.CH 3 ).COOEt + NaCl 

CHNa(COOEt) 2 + CH 3 .COCl = CH(CO.CH 3 )(COOEt) 2 + NaCl, 
and with halogen derivatives of esters, such as ethyl chloracetate 
(pp. 240-41) ; the compounds thus obtained undergo hydrolysis in 
much the same way as the simple alkyl derivatives of the two esters. 



CHAPTER XII. 

ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ARSENIC, 
SILICON, ZINC, MERCURY, AND OTHER ELEMENTS. 

Amines. 

Many of the compounds described in the preceding pages 
may be conveniently considered as having been derived from 
simple inorganic compounds; the alcohols and ethers, for 
example, may be regarded as derivatives of water, the 
mercaptans and sulphides as derivatives of sulphuretted 
hydrogen, 

H-O-H C 2 H 5 -OH C 2 H 5 .0-C 2 H 5 

H'S-H Cfjiig'SH C 2 H5S < C 2 ri5. 

In a similar manner the hydrides of many other elements may 
be directly or indirectly converted into organic compounds by 
the substitution of one or more alkyl groups for an equivalent 
quantity of hydrogen ; from ammonia, for example, a very 
important class of strongly basic substances, termed amines, 
may be obtained, these compounds being classed as primary, 
secondary, or tertiary amines, according as 1, 2, or 3 atoms of 
hydrogen in ammonia have been displaced by alkyl groups. 

Primary. Secondary. 

Methylamine, NH 2 -CH 3 Dimethylamine, NH(CH 8 ) 2 

Ethylamine, NH 2 -C 2 H 5 Diethylamine, NH(C 2 H 5 ), 

Propylamine, NH 2 -C 3 H 7 Dipropylarnine, NH(C 3 H 7 ) 2 



ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 205 

Tertiary. 

Trimethylamine, N(CH 3 ) 3 
Triethylamine, N(C 2 H 5 ) 3 
Tripropylamine, ^(CgHi^g 

The methods of formation and general character of the amines 
will, perhaps, be best understood from a description of the 
ethyl compounds. 

Ethylamine, NH 2 -C 2 H 5 , was first obtained by Wiirtz, by 
distilling ethyl isocyanate (p. 296) with potash, the change 
being analogous to that which occurs in the case of hydrogen 
isocyanate (p. 295), 

CO:N.C 9 H, + 2KOH = NH 2 -C 2 H 5 + K 2 C0 3 



CO:NH + 2KOH - NH 3 + K 2 C0 3 . 
It is formed when methyl cyanide (acetonitrile) is treated 
with nascent hydrogen, generated from zinc and sulphuric 
acid (Mendius' reaction), or, better, from alcohol and sodium, 

CH 3 -CN + 4H = CH 3 .CH 2 .NH 2 . 

It is also produced when ethyl chloride, bromide, or iodide is 
heated at about 100 in closed vessels with alcohol which has 
been saturated with ammonia (Hofmann) ; the halogen acid 
produced during the interaction combines with the amine, 
forming a salt, 

C 2 H 5 I + NH 3 - NH 2 -C 2 H 5 , HI. 

Ethylamine is prepared by mixing propionamide(l mol.) with 
bromine (1 mol.), and then adding a 10 per cent, solution of 
potash until the colour of the bromine disappears ; the solution 
of the brompropionamide which is thus produced, 
CgHj-CO-NHa + Br 2 + KOH = C 2 H 5 .CO-NHBr + KBr + H 2 0, 
is now gently warmed with excess of potash, when the brom- 
amide is converted into ethylamine (Hofmann), 
C 2 H 5 .CO-NHBr + 3KOH = C 2 H 5 -NH 2 + KBr + K 2 C0 3 + H 2 0. 

In the conversion of propion amide into ethylamine one atom of 
carbon and one atom of oxygen are taken away, and a derivative of 
propionic acid is converted into what may be regarded as a deriva- 
tive of acetic acid, since ethylamine is readily converted into ethyl 



I 

206 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 

alcohol and the latter into acetic acid ; it is possible, therefore, to 

transform propionic into acetic acid, 

CH 3 -CH 2 .COOH CH 3 .CH 2 .CO.NH 2 CH 3 .CH 2 .NH 2 CH 3 -CH 2 .OH 

Propionic Acid. Propionamide. Ethylamine. Ethyl Alcohol. 

CH 3 -COOH. 

Acetic Acid. 

As, moreover, the amides of other fatty acids behave in this respect 
like propionamide, it is clear that a given fatty acid may be con- 
verted into the next lower homologue, and so on down the series. 

Conversely, a given fatty acid may be transformed into the next 
higher homologue in the following manner : The calcium salt of 
the acid is distilled with calcium formate, and the resulting alde- 
hyde converted into the corresponding alcohol by reduction ; the 
alcohol is then transformed into the iodide, the latter treated with 
potassium cyanide, and the resulting cyanide hydrolysed with 
alkalies or mineral acids, 
CH 3 .COOH CH 3 .CHO CH 3 .CH 2 .OH CH 3 -CH 2 I CH 3 .CH.CN 

Acetic Acid. Acetaldehyde. Ethyl Alcohol. Ethyl Iodide. Ethyl Cyanide. 

CH 3 .CH 2 .COOH. 

Propionic Acid. 

The cyanide may be converted into the acid in another way ; it is 
first reduced with sodium and alcohol, yielding an amine, from which 
the fatty acid is obtained in the manner already stated. 

Primary amines may also be obtained by reducing the nitro- 
paraffins, 

CH 3 -N0 2 + 6H = CH 3 .NH 2 + 2H 2 O, 

and by heating the alkyl nitrates with alcoholic ammonia, 
C 3 H 7 .O.N0 2 + NH 3 =C 3 H 7 .NH 2 , HNO y 

Ethylamine is a colourless, mobile, inflammable liquid of sp. 
gr. 0-689 at 15, and boils at 18-7; it is soluble in water in 
all proportions, and the solution, like the liquid itself, has a 
pungent, slightly fish-like odour, distinguishable from that of 
ammonia only with difficulty. An aqueous solution of ethyl- 
amine might, in fact, be easily mistaken for a solution of 
ammonia, so closely do they resemble one another in properties ; 
the former, like the latter, has a strongly alkaline reaction, and 
gives, especially on warming, a pungent-smelling gas, which 
fumes when brought into proximity with concentrated hydro- 
chloric acid ; it precipitates metallic hydroxides from solutions 
of their salts, and neutralises even the most powerful acids, 



ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 207 

forming salts, which are readily soluble in water. Ethyl- 
amine, therefore, is an organic base, and its basic properties 
are even more pronounced than those of ammonia ; the salts 
of ethylamine, however, are decomposed by the hydroxides 
and carbonates of sodium and potassium. In spite of the 
fact that ethylamine is so readily soluble in water, it separates 
from the solutions as an oil on the addition of a large quantity 
of solid potash or potassium carbonate ; it is very hygro- 
scopic, and readily absorbs carbon dioxide from the air, 
forming with it a salt.* 

Although, speaking generally, ethylamine is very stable, it 
is rapidly converted into ethyl alcohol on treatment with 
nitrous acid in aqueous solution, nitrogen being liberated, 
C 2 H 5 -NH 2 + HO-NO = C 2 H 5 .OH + H 2 + N 2 ; 

this reaction is exactly analogous to that which occurs when 
ammonia and nitrous acid (ammonium nitrite) are heated 
together, 

NH 4 N0 2 or tf H 3 + HO-NO = 2H-OH + N 2 . 

Ethylamine is also quickly changed when it is warmed with 
chloroform and alcoholic potash. The intensely disagreeable 
smell of the product (ethylcarbylamine, compare p. 294) is at 
once recognisable, and affords a sure indication of the presence 
of a primary amine (Hofmann's carbylamine reaction), 

C 2 H 5 -NH 2 + CHC1 3 + 3KOH C 2 H 5 -NC + 3KC1 + 3H 2 0. 

The two reactions just mentioned are characteristic of all 
primary amines, and are of considerable practical importance ; 
the first is. employed for the conversion of the primary 
amines into hydroxy-compounds, the second for their 
detection. 

Ethylamine is a monacid base, and, like ammonia; forms salts 
by direct combination, in virtue of the possible pentavalency 
of the nitrogen atom ; these salts are all soluble in water, and 
some of them, like those of ammonia, readily sublime, even 

* Probably not a carbonate, but a carbamate(p. 301), CO^Qjj ^ -^ 



208 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 

at ordinary temperatures ; they usually differ from ammonium 
salts in being soluble in alcohol, a property which is fre- 
quently made use of in isolating the amine. 

Ethylamine hydrochloride, C 2 H 5 .NH 3 C1, or C 2 H 5 -NH 2 , HC1, 
as usually written, crystallises in large plates, melts at about 
80, and is deliquescent. The sulphate, 2C 2 H 5 .KH 2 , H 2 S0 4 , 
has similar properties. The halogen salts, like those of 
ammonia, form double salts with many other metallic halogen 
salts ; of these compounds the platiniclilorides and the auri- 
chlorides are the most important ; they correspond with the 
ammonium double salts of similar composition, 

Ethylamine platinichloride, (C 2 H 5 -NH 2 ) 2 , H 2 PtCl 6 
Ammonium platinichloride, (NH 3 ) 2 , H 2 PtCl 6 

Ethylamine aurichloride, C 2 H 5 -NH 2 , HAuCl 4 
Ammonium aurichloride, NH 3 , HAuCl 4 . 

These organic platinum and gold salts are usually yellow, 
orange, or red, and are generally much more sparingly soluble 
in water than the simple salts ; for the latter reason they are 
very serviceable in detecting and isolating the amines ; on 
ignition they give a residue of pure metal. 

Diethylamine, NH(C 2 H 5 ) 2 , is formed when ethyl iodide 
is heated with alcoholic ammonia, just as described in the 
case of ethylamine; one molecule of the hydrogen iodide 
produced combines with the base to form a salt, the other 
uniting with the excess of ammonia, 

2C 2 H 5 I + NH 3 = NH(C 2 H 5 ) 2 , HI + HL 

Diethylamine is a colourless, inflammable liquid, boiling at 
56 ; it is a stronger base than ethylamine, which it resembles 
very closely in smell, solubility, &c., and also in forming 
simple and double salts. It is readily distinguished from 
ethylamine inasmuch as it does not give the carbylamine 
reaction; its behaviour with nitrous acid is also totally 
different from that of ethylamine, since, instead of being con- 
verted into an alcohol, it yields diethylnitrosamine, 

(C 2 H 5 ) 2 NH + HO.JSTO = (C 2 H 5 ) 2 N-NO + H 2 0. 



ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 209 

All secondary amines behave in this way ; that is to say, on 
treatment with nitrous acid, they are converted into nitros- 
amines by the substitution of the monovalent nitroso-group 
-NO for the atom of hydrogen which is directly united with 
nitrogen. 

When a nitrosamine is mixed with phenol (Part II. p. 404) and 
concentrated sulphuric acid, it gives a dark -green solution which, 
after diluting with water, becomes red, and on adding excess of 
alkali, assumes a beautiful and intense blue or green colour ; this 
reaction (Liebermann's, or the nitroso-reaction) affords a means 
of detecting, not only a nitrosamine, but also a secondary amine, 
as the latter is convertible into the former. 

Diethylamine hydrochloride, (C 2 H 5 ) 2 NH, HC1, is colourless, and 
readily soluble in water ; its platinichloride, [(C 2 H 5 ) 2 NH] 2 , H 2 PtCl 6 , 
and aurichloride, (C 2 H 5 ) 2 NH, HAuCl 4 , are orange, and less readily 
soluble. 

Triethylamine, N(C 2 H 5 ) 3 , like the primary and secondary 
amines, is produced when ethyl iodide is heated with alcoholic 
ammonia, 

3C 2 H 5 I + NH 3 = N(C 2 H 5 ) 3 , HI + 2HL 

It is a pleasant-smelling liquid, boiling at 89, and except 
that it is more sparingly soluble in water, it resembles the 
primary and secondary compounds in most ordinary properties. 
It does not give the carbylamine reaction, and is not acted 
on by nitrous acid at ordinary temperatures, so that it is 
readily distinguished from the primary and secondary amines ; 
other tertiary amines resemble triethylamine in these respects. 
The salts of triethylamine correspond with those of the other 



Triethylamine, and other tertiary amines, combine directly 
with one molecule of the alkyl halogen compounds, yielding 
salts corresponding with those of ammonium, 

JST(C 2 H 5 ) 3 + C 2 H 5 I = N(C 2 H 5 ) 4 I NH 3 + HI = NH 4 I. 
The bases contained in these salts are not expelled by potash 
or soda, even on boiling, because they are not volatile ; when, 
however, aqueous solutions of their halogen salts are shaken 
with freshly precipitated silver hydroxide, double clecom- 

Org. N 



210 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 

position results, and hydroxy-compounds, corresponding with 
ammonium hydroxide, are formed, 

N(C 2 H 5 ) 4 I + Ag-OH = N(C 2 H 5 ) 4 .OH + Agl 
NH 4 I + Ag-OH = NH 4 -OH + Agl. 

The hydroxides obtained in this way are termed quaternary 
ammonium bases, or tetralkylammonium hydroxides ; although, 
in constitution, they are similar to ammonium hydroxide, 
they differ from the latter in several important respects, and 
resemble rather the hydroxides of sodium and potassium. 

Tetrethylammonium hydroxide, N(C 2 H 5 ) 4 -OH, for ex- 
ample, is a crystalline, deliquescent substance, and has only a 
faint smell; it has a powerful alkaline reaction, absorbs carbon 
dioxide from the air, and liberates ammonia from ammonium 
salts ; when strongly heated it is resolved into triethylamine 
and ethyl alcohol, or its decomposition products, 

N(C 2 H 5 ) 4 .OH = N(C 2 H 5 ) 3 + C 2 H 4 + H 2 0. 

The salts of tetrethylammonium hydroxide, such as the 
iodide (see above), may also be obtained by treating the 
hydroxide with acids ; they are mostly crystalline. 

The tetralkylammonium halogen salts undergo decom- 
position or dissociation on dry distillation, yielding a tertiary 
amine and an alkyl halogen salt, just as ammonium chloride 
is resolved into ammonia and hydrogen chloride, 

N(C 2 H 5 ) 4 C1 = N(C 2 H 5 ) 3 + C 2 H 6 G1 NH 4 C1 = NH 3 + HC1. 

Under ordinary circumstances the halogen ethereal salt, 
being much more volatile than the tertiary amine, can be 
separated from the latter before recombination takes place. 

In a similar manner the halogen salts of some tertiary 
amines may be converted into secondary, and those of 
secondary into primary, amines, 



= ]S T (CH 3 )H 2 + CH 3 C1. 

The three ethylamines and the tetrethylammonium com- 
pounds may be taken as typical examples of the several 



ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 211 

classes of alkyl derivatives of ammonia ; the corresponding 
methyl bases, and those of the higher alkyl radicles, are pre- 
pared by methods so similar to those described in the case of 
the ethylamine compounds, and have properties so closely 
resembling those of the latter, that a detailed description 
would be of little value. 

Methylamine, NH 2 -CH 3 ; dimethylamine, NH(CH 3 ) 2 ; and tri- 
methylamine, N(CH 3 ) 3 , are usually produced in small quantities 
during the decomposition of nitrogenous organic substances, and 
occur in herring brine, the last named especially in large relative 
proportions. Dimethylamine and trimethylamine are prepared on 
the large scale by distilling the waste products obtained in refining 
beet-sugar, and are used in considerable quantities for various 
technical purposes ; trimethylamine is employed in the manufac- 
ture of potassium carbonate, and its hydrochloride is used in the 
preparation of methyl chloride (p. 175). 

The physical properties of the amines undergo a gradual change 
with increasing molecular weight, just as is the case in other series ; 
the boiling-points of the four simplest normal primary amines may 
be taken as an illustration : 

Methylamine, CH 3 .NH 2 B.p. -6 

Ethylamine, C 2 H 5 .NH 2 +19 

Propylamine, C 3 H 7 -NH 2 49 

Butylamine, C 4 H 9 .NH 2 76 

The higher amines, like the higher ethers, esters, &c., exist in 
various isomeric forms : there are, for example, three compounds 
of the molecular formula C 3 H 9 N (see below). The amines, like the 
ethers, may be classed into simple amines, such as propylamine, 
C 3 H 7 'NH 2 , diethylamine, (C 2 H 5 ) 2 NH, &c., and mixed amines, 
such as methyletUylamine, NH(CH 3 )-C 2 H 5 , dimethylethylamine, 
N(CH 3 ) 2 -C 2 H 5 , according as they contain alkyl-groups of the same 
or of different kinds. 

Preparation and Identification of Amines. Some of the 
principal methods actually used for the preparation of 
primary amines have already been described namely, the 
reduction of the cyanides or nitriles (p. 205 ; compare also 
p. 294) and the decomposition of the amides with bromine 
and potash (p. 205), both of which are important general 
reactions. 



212 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 

Primary amines are also prepared by reducing oximes with 
zinc dust and acetic acid, or with sodium and alcohol, 

(CH 3 ) 2 C:NOH + 4H = (CH 3 ) 2 CILNH 2 + H 2 0, 
and by reducing hydrazones with zinc dust and acetic acid. 

The compounds formed by the combination of aldehydes with 
ammonia are also reduced to amines when treated with zinc and 
hydrochloric acid in the cold, 



but it is unusual for the hydroxyl-group to be displaced by hydrogen 
under such conditions, and a change of this kind is generally 
brought about only on heating with hydriodic acid (p. 55). 

In all these methods the product is usually isolated by distilling 
in steam (after making the solution strongly alkaline), collecting in 
hydrochloric acid, evaporating to dryness, and then distilling the 
hydrochloride with powdered caustic potash. 

Secondary and tertiary amines are prepared by heating the 
alkyl bromides or iodides with alcoholic ammonia, but as 
primary bases and tetralkylammonium compounds are also 
obtained, the separation of the four products is a troublesome 
matter. For this reason it is often more convenient to pre- 
pare the primary amine by one of the methods given above, 
and then to heat it with the alkyl bromide or iodide in 
presence of excess of potash, when reactions such as the 
following occur, 

C 2 H 5 .NH 2 + C 2 H 5 I + KOH = (C 2 H 5 ) 2 NH + KI + H 2 
(C 2 H 5 ) 2 NH + C 2 H 5 I + KOH = (C 2 H 5 ) 8 N + KI + H 2 



A primary may thus be converted into a secondary base, and 
the latter into a tertiary base, which finally forms a tetralkyl- 
ammonium salt; on subsequently distilling in steam, the 
secondary and tertiary bases pass over and the stable tetralkyl- 
ammonium salt remains behind. 

The latter may usually be isolated by neutralising this residue 
with hydrochloric acid, evaporating to dryness, and extracting with 
alcohol. The distillate containing the amines may be neutralised 
with some acid and the mixture of salts separated by fractional 



ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 213 

crystallisation ; the platinichlorides and aurichlorides are often used 
for this purpose, and most organic bases also form with picric acid 
(Part II. p. 406) sparingly soluble compounds which are very 
useful in such cases. 

A tertiary base may generally be separated from a secondary 
base by converting the latter into its nitroso-derivative (p. 208), 
and then extracting this neutral product from the acid solution 
by shaking with ether ; the tertiary base is then liberated by 
adding potash, and distilled in steam, whilst the secondary 
base may be recovered by decomposing the nitroso-derivative 
with boiling hydrochloric acid, 

(C 2 H 5 )N-NO + H 2 = (C 2 H 5 ) 2 .NH + HO-NO. 
A tertiary base may also be separated from a primary or 
secondary base by making use of the fact that the two latter 
interact readily with acid chlorides, giving neutral substituted 
amides, 

C 2 H 5 .NH 2 + CHg-COCl = C 2 H 5 .NH.CO-CH 3 + HC1 
(C 2 H 5 ) 2 NH +H 3 .COC1 = (C 2 H 5 ) 2 N.CO.CH 3 + HC1, 

whereas a tertiary base is not acted on ; by extracting the acid 
solution of the product only the neutral amide is removed. 

In order to find out whether a given amine is a primary, 
secondary, or tertiary base, Hofmann's carbylamine reaction is 
first tried ; a most offensive odour due to the formation of a 
carbylamine or isocyanide (p. 294) shows the presence of a 
primary amine. If this test give no result, the base is 
dissolved in hydrochloric acid and an aqueous solution of 
potassium nitrite is gradually added ; the separation of an 
oily nitrosamine (which can be further characterised by 
Liebermann's reaction) proves the presence of a secondary 
amine. A tertiary base does not give either of these reactions, 
and does not interact with acid chlorides. 

As most amines are liquid, and consequently difficult to identify 
as such, except by a determination of the boiling-point, they are 
usually characterised by converting them into crystalline deriva- 
tives such as their hydrochlorides, platinichlorides, aurichlorides, 
picrates (see above), acetyl derivatives, or benzoyl derivatives (Part II. 



214 ALKYL COMPOUNDS OP NITROGEN, PHOSPHORUS, ETC. 

p. 432) ; if this be insufficient an analysis of the platinichloride or 
aurichloride is usually made (p. 34). 

Phosphines. 

Since phosphorus and nitrogen belong to the same natural 
group of elements, it might be expected that phosphoretted 
hydrogen, PH 3 , like ammonia, would be capable of yielding 
substitution products analogous to the amines. As a matter 
of fact, the phosphines, or alkyl substitution products of phos- 
phorus trihydride, are readily obtained by heating the alkyl 
iodides with phosphonium iodide in presence of zinc oxide 
(which combines with the hydrogen iodide produced in the 
reaction). In the case of ethyl iodide, for example, salts of 
ethylphosphine and dietTiylpTiosphine, corresponding with those 
of the primary and secondary amines respectively, are formed, 

2PH 4 I + 2C 2 H 5 I + ZnO = 2[PH 2 -C 2 H 5 , HI] + ZnI 2 + H 2 
PH 4 I + 2C 2 H 5 I + ZnO = PH(C 2 H 5 ) 2 , HI + ZnI 2 + H 2 0. 

Tertiary phosphines, such as triethylphosphine, are not pro- 
duced under the above conditions, but may be prepared by 
heating the alkyl iodides with phosphonium iodide alone ; 
as in the case of the corresponding amines, the tertiary phos- 
phines combine with alkyl iodides, forming salts of quaternary 
bases, such as tetrethylphosphonium iodide, so that the pro- 
duct is a mixture of two organic compounds, 

PH 4 I + 3C 2 H 5 I = P(C 2 H 5 ) 3 , HI + SHI 



With the exception of methylphosphine, PH 2 -CH 3 , which is 
a gas, the primary, secondary, and tertiary phosphines are 
colourless, volatile, highly refractive, very unpleasant-smelling 
liquids ; they differ from the amines in smell, in being, as a 
rule, insoluble, or only sparingly soluble, in water (PH 3 , un- 
like NH 3 , is only sparingly soluble), and in readily undergoing 
oxidation on exposure to the air ; in many cases so much 
heat is developed during this process that the compound takes 
fire that is to say, many of the phosphines are spontaneously 



ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 215 

inflammable. When tertiary phosphines undergo slow oxida- 
tion in presence of air, they are converted into stable oxides, 
such as triethylphosphine oxide, P(C 2 H 5 ) 3 0.* 

Although phosphoretted hydrogen is only a feeble base 
compared with ammonia, and forms salts, such as phosphonium 
iodide, PH 4 I, which are decomposed even by water, each suc- 
cessive substitution of an alkyl-group for an atom of hydrogen 
is accompanied by an increase in basic properties, just as in 
the case of the amines. Salts of the primary phosphines, 
such as ethylphospJiine hydriodide, PH 2 -C 2 H 5 , HI, are almost, 
if not quite, as unstable as those of hydrogen phosphide, and 
are decomposed into acid and base on treatment with water ; 
they may thus be separated from the more stable salts of the 
secondary and tertiary phosphines, such as diethylphospTiine 
hydriodide, PH(C 2 H 5 ) 2 , HI, and triethylphosphine hydriodide, 
P(C 2 H 5 ) 3 , HI, which are not acted on by water as a rule, 
but are readily decomposed by potash and soda. Salts of 
the tetralkylphosphonium compounds, such as tetrethylphos- 
plionium iodide, P(C 2 H 5 ) 4 T, are not acted on by water or by 
alkalies, but on treatment with moist silver hydroxide they 
are converted into quaternary phosphonium hydroxides, 

P(C 2 H 5 ) 4 I + Ag.OH = P(C 2 H 5 ) 4 .OH + Agl. 

These compounds have a strong alkaline reaction, readily 
absorb carbon dioxide, and dissolve freely in water; they are, 
in fact, similar in properties to the hydroxides of the fixed 
alkalies, and their salts are much more stable than the phos- 
phine salts, just as those of the corresponding tetralkyl- 
ammonium bases are more stable than those of ammonia. 

Arsines. 

The hydrogen atoms of the hydrides of arsenic and anti- 
mony, and the chlorine atoms of bismuth trichloride, may be 
(indirectly) displaced by alkyl groups ; but although in the 

* Tertiary amines give similar oxidation products, termed oxamines, on 
treatment with hydrogen peroxide. 



216 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 

case of arsenic primary and secondary arsines, As(CH 3 )H 2 
and As(CH 3 ) 2 H, are known, the principal alkyl compounds 
of these elements correspond with the tertiary amines, and 
have the composition AsE 3 , SbR 3 , and BiR 3 respectively. 

The tertiary arsines are obtained by treating arsenious 
chloride with the zinc alkyl compounds (p. 220), or by heat- 
ing the alkyl iodides with sodium arsenide, 

2AsCl 3 + 3Zn(C 2 H 5 ) 2 = 2 As(C 2 H 5 ) 3 + 3ZnCl 2 
AsNa 3 + 3CH 3 I = As(CH 3 ) 3 + 3NaI. 

Triethylarsine, As(C 2 H 5 ) 3 , may be described as a typical 
arsine. It is a colourless, very unpleasant-smelling, highly 
poisonous liquid, and is only sparingly soluble in water ; it 
fumes in the air, and takes fire when heated, but does not 
ignite spontaneously. It differs from the amines and phos- 
phines in being a neutral compound, and, like arseniuretted 
hydrogen, it does not form salts with acids ; it resembles tho 
tertiary amines and phosphines in combining readily with 
alkyl iodides, forming salts of quaternary arsonium hydroxides, 
As(C 2 H 5 ) 3 + C 2 H 5 I = As(C 2 H 5 ) 4 I. 

Tetrethylarsonium iodide, As(C 2 H 5 ) 4 I, for example, is a 
crystalline substance, and, like other quaternary organic salts, 
it is not decomposed by potash, although it interacts with 
silver hydroxide, giving tetrethylarsonium hydroxide, 
As(C 2 H 5 ) 4 I + Ag-OH = As(C 2 H 5 ) 4 .QH + Agl. 

This substance has a strong alkaline reaction, and neut- 
ralises even the most powerful acids; here, again, as in 
the case of nitrogen and phosphorus, the basic character 
increases with the number of alkyl groups in the molecule. 

The tertiary arsines resemble the tertiary phosphines in 
readily undergoing oxidation on exposure to the air, forming 
oxides such as triethylarsine oxide, As(C 2 H 5 ) 3 0. 



The tertiary stibines, the organic derivatives of antimony, 
are on the whole similar to those of arsenic, but have 
not been so carefully investigated ; the tertiary bismuth 



ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 217 

compounds, such as Bi(CH 3 ) 3 , cannot be converted into 
quaternary hydroxides, corresponding with those of arsenic 
and antimony, and owing to the more pronounced metallic 
character of bismuth, its compounds resemble rather those of 
the metals zinc, mercury, &c. (p. 220). 

Derivatives of the Ar sines. Tertiary arsines combine directly 
with two atoms of a halogen, forming compounds, such as 
triethylarsine dichloride, As(C 2 H 5 ) 3 Cl 2 , in which the arsenic 
atom is pentavalent ; these substances are decomposed on 
heating, yielding an alkyl halogen compound and a halogen 
derivative of a secondary arsine, 

As(C 2 H 5 ) 3 Cl 2 - As(C 2 H 5 ) 2 Cl + C 2 H 5 C1. 

These halogen derivatives of the secondary compounds 
also combine with one molecule of a halogen, 
Cl + C1 = 



and the products, on heating, are decomposed into dihalogen 
derivatives of primary arsines, 

As(C 2 H 5 ) 2 Cl 3 = As(C 2 H 5 )Cl 2 + C 2 H 5 C1. 

The derivatives of dimethylarsine are of considerable 
interest, and have been very carefully investigated by Bunsen. 

Dimethylarsine oxide, or cacodyl oxide, 



is formed when a mixture of equal parts of arsenious oxide 
and potassium acetate is submitted to dry distillation ; during 
the operation highly poisonous gases are evolved, and an oily 
liquid collects in the receiver, 

As 4 6 + 8CH 3 .COOK = 2As 2 (CH 3 ) 4 + 4K 2 C0 3 + 4C0 2 . 

This liquid has an intensely obnoxious smell,* and is ex- 
cessively poisonous, for which reasons its preparation, except 
in minute quantities, should not be attempted ; its formation 
may, however, be used as a test for acetates if due care be 
taken, as the substance is readily recognisable by its smell. 

Cacodyl oxide boils at 1 20, and is insoluble in water ; the 

* The name cacodyl is derived from the Greek ***$?, 'stinking.' 



218 ALKYL COMPOUNDS OP NITROGEN, PHOSPHORUS, ETC. 

substance prepared in the above-mentioned manner is spon- 
taneously inflammable owing to the presence of cacodyl, but 
the pure compound is not. In chemical properties cacodyl 
oxide resembles the feebly basic metallic oxides; it has a 
neutral reaction, but interacts readily with acids, forming salts, 
such as cacodyl chloride and cacodyl cyanide, As(CH 3 ) 2 -CN, 

2HC1 = 2As(CH 3 ) 2 Cl + H 2 O. 

When cacodyl chloride is heated with zinc in an atmos- 
phere of carbon dioxide, it yields cacodyl or diarsenic tetra- 
methyl, a change which is analogous to the formation of 
ethane from methyl iodide, 

2As(CH 3 ) 2 Cl + Zn = As(CH 3 ) 2 - As(CH 3 ) 2 + ZnCl 2 

2CH 3 I + 2Na = CH 3 - CH 3 + 2XaI. 

Cacodyl, like the oxide, is a colourless, excessively poison- 
ous liquid, and has an intensely disagreeable smell ; it takes 
fire on exposure to the air. 

Cacodylic acid, (CH 3 ) 2 AsO-OH, is formed when cacodyl oxide is 
oxidised with mercuric oxide, 

+ 2Hg + Ha = 2 ( CH 3) 2 AsO.OH + 2Hg ; 



it is a crystalline, odourless substance, and seems to be non- 
poisouous. 

Organic Silicon Compounds. 

The organic compounds of silicon are of exceptional in- 
terest, because their study exhibits in a very strong light the 
close relationship between silicon and carbon. Just as the 
paraffins may be considered as derived from the hydride, 
methane, CH^ by the substitution of alkyl groups for 
hydrogen, so may the analogous silicon compounds be regarded 
as derivatives of silicon hydride, SiH 4 . Up to the present, 
however, only those compounds containing four alkyl 
radicles have been prepared, as, for example, silicon tetra- 
methyl, Si(CH 3 ) 4 , corresponding with carbon tetramethyl or 
tetramethylmethane, C(CH 3 ) 4 ; substances such as SiH(CH 3 ) 3 , 






ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 219 

SiH 2 (CH 3 ) 2 , &c., which would be analogous to the hydro- 
carbons CH(CH 3 ) 3 , CH 2 (CH 8 ) 2 , &c., are not known. 

Silicon tetramethyl, Si(CH 3 ) 4 , is produced when silicon 
tetrachloride is heated with zinc methyl, 

SiCl 4 + 2Zn(CH 3 ) 2 = Si(CH 3 ) 4 + 2ZnCl 2 . 

It is a colourless, mobile, volatile liquid, boiling at 30, and 
has properties very similar to those of tetramethylmethane. 

Silicon tetrethyl, Si(C 2 H 5 ) 4 , may be obtained from silicon 
tetrachloride and zinc ethyl in a similar manner, and also 
by heating a mixture of silicon tetrachloride and ethyl 
bromide, dissolved in ether, with sodium, 

SiCl 4 + 4C 2 H 5 Br + 8Na = Si(C 2 H 5 ) 4 + 4NaCl + 4NaBr ; 

it boils at 153, and closely resembles the normal paraffin, 
nonane, C 9 H 20 , in properties. It may, in fact, be regarded 
as derived from the as yet unknown isomeride of nonane, 
tetrethylmethane, C(C 2 H 5 ) 4 , by the substitution of one atom 
of silicon for one atom of carbon; for this reason it is 
sometimes named silicononane. 

The great similarity between silicononane and nonane is strik- 
ingly shown by the following facts : Silicononane, like nonane, is 
a colourless liquid, insoluble in, and specifically lighter than, water ; 
like nonane, it is a very stable substance, and is not acted on by 
nitric acid or caustic alkalies. On treatment with chlorine it 
behaves like a paraffin, and yields the substitution product silico- 
nonyl chloride, Si(C 2 H 5 ) 3 -C 2 H 4 Cl, a colourless liquid, boiling at 185 ; 
this chloride closely resembles the alkyl chlorides in properties, 
and, like the latter, interacts with silver acetate, giving silicononyl 
acetate, 

Si(C 2 H 5 ) 3 .C 2 H 4 Cl + C 2 H 3 2 Ag= Si(C 2 H 5 ) 3 .C 2 H 4 .C 2 H 3 2 + AgCl. 

This ethereal salt is readily hydrolysed by alkalies, yielding 
silicononyl alcohol, just as ethyl acetate gives ethyl alcohol, 

Si(C 2 H 5 ) 3 .C 2 H 4 -C 2 H 3 O 2 + KOH = Si(C 2 H 5 ) 3 .C 2 H 4 -OH + C 2 H 3 O 2 K ; 
this alcohol, again, is a colourless, neutral liquid, boiling at 190, 
analogous in most respects to the higher alcohols of the general 
formula C n H 2n +i-OH. 

Organic silicon compounds, such as Si 2 (C 2 H 5 ) 6 , corresponding with 
, are known, but are of less importance, 



220 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 

Or gano- Metallic Compounds. 

Many of the metals, such as mercury, zinc, tin, and lead, 
form compounds with alkyl-groups, although their hydrides 
are unknown. These alkyl compounds are named 'organo- 
metallic ' compounds, but there is no sharp division between 
them and the alkyl compounds of other elements, just as 
there is none between the metals and non-metals. If, in fact, 
the alkyl compounds of elements belonging to the same 
natural group be considered, it will be evident that they show 
a gradual change in properties, just as do the elements them- 
selves, and pass into organo-metallic compounds without any 
abrupt transition. The compounds of the elements of the 
fourth group, for example, such as 

C(CH 3 ) 4 Si(CH 3 ) 4 Sn(CH 3 ) 4 Pb(CH 3 ) 4 , 

may be divided into two fairly distinct classes ; but in the 
case of those of the elements of the fifth group, 

N(CH 3 ) 3 P(CH 8 ) 3 As(CH 3 ) 3 Sb(CH 3 ) 3 Bi(CH 3 ) 3 , 

it is practically impossible to say which of them, if any, 
should be classed as organo-metallic compounds. 

The zinc alkyl compounds, which were discovered by 
Frankland, are perhaps of the greatest importance, on account 
of their frequent employment in the synthesis of other 
organic substances, of which many examples have already 
been given ; their properties, moreover, are in many respects 
typical of those of other organo-metallic compounds. 

Zinc ethyl, Zn(C 2 H 5 ) 2 , is formed when ethyl bromide or 
iodide is digested with an alloy of sodium and zinc, 

ZnNa 2 + 2C 2 H 5 I = Zn(C 2 H 5 ) 2 + 2NaI. 

It is usually prepared by heating zinc with ethyl iodide 
in an atmosphere of carbon dioxide; the first product is a 
colourless, solid substance (zinc ethiodide), containing iodine, 



ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 221 

but on heating more strongly a second change occurs, and 
zinc ethyl is formed, 



2Zn< j = Zn(C 2 H 5 ) 2 + ZnI 2 . 

Zinc filings (100 grams) and an equal weight of ethyl iodide are 
placed in a flask connected with a reflux condenser, and the air is 
completely expelled from the apparatus by passing a stream of dry 
carbon dioxide through a narrow tube which runs through the con- 
denser to the bottom of the flask. The condenser is then quickly 
fitted with a cork through which passes a tube, dipping under mer- 
cury, in order to prevent access of air ; the materials and the 
apparatus must be perfectly dry. 

The flask is now heated on a water-bath, when a rapid evolution 
of gas (butane) takes place, and the white intermediate product is 
gradually formed ; after two to three hours' time the interaction is 
at an end. When cold, the flask is quickly fitted with a cork 
and glass tubes (just as in an ordinary wash-bottle), and the smaller 
tube is connected with a condenser; the flask is then heated in 
an oil-bath, and the zinc ethyl distilled, a stream of dry carbon 
dioxide being passed through the longer tube into the apparatus 
during the whole operation ; the distillate is collected in a vessel 
which can be easily sealed. 

Zinc ethyl is a colourless liquid, and boils at 118 without 
decomposing; it must be distilled in an atmosphere free 
from oxygen, since it inflames spontaneously on exposure to 
the air, burning with a luminous, greenish flame, and emitting 
clouds of zinc oxide. It decomposes water with great 
energy, yielding ethane and zinc hydroxide, 

Zn(C 2 H 5 ) 2 + 2H 2 = 2C 2 H 6 + Zn(OH) 2 , 

and it is also decomposed by alcohol, but not so quickly 
as by water, 

OP TT 

Zn(C 2 H 6 ) 2 + 2C 2 H 5 .OH = 2C 2 H 6 + Zn<^g. 

Zinc ethyl interacts readily with all substances containing 
the hydroxyl-group, and also with almost all halogen com- 
pounds, whether organic or inorganic, as, for example, with 
acid chlorides (pp. 108 and 139), alkyl halogen compounds 
(p. 68), and metallic chlorides ; for these reasons, it is exten- 



222 ALKYL COMPOUNDS OF NITROGEN, PHOSPHORUS, ETC. 

sively used in the synthesis of paraffins, ketones, tertiary 
alcohols, &c., as well as in the preparation of other organo- 
metallic compounds. 

Zinc methyl, Zn(CH 3 ) 2 , resembles zinc ethyl in most 
respects, and is prepared by heating methyl iodide with zinc, 
or, better, with the zinc-copper couple. It is a colourless 
liquid, boiling at 46, and is decomposed by water, yielding 
methane and zinc hydroxide. 

Mercuric ethyl, Hg(C 2 H 5 ) 2 , is formed when zinc ethyl is 
treated with mercuric chloride, 

Zn(C 2 H 5 ) 2 + HgCl 2 = Hg(C 2 H 5 ) 2 + ZnCl 2 , 
but it is usually prepared by shaking ethyl iodide with 
sodium amalgam, 

HgNa 2 + 2C 2 H 5 I = Hg(C 2 H 5 ) 2 + 2NaI. 

Mercuric ethyl is a colourless, very heavy liquid, of sp. gr. 
244; it boils at 159 without decomposing, and is not 
spontaneously inflammable at ordinary temperatures, although 
it ignites readily when strongly heated. It is much less 
active than zinc ethyl, does not oxidise on exposure to the air, 
and is not decomposed by water, in which it is only sparingly 
soluble ; both the liquid and its vapour are highly poisonous. 
On treatment with halogen acids, mercuric ethyl is converted 
into salts, analogous in some respects to the halogen salts of 
the alkali metals, 

Hg(C 2 H 5 ) 2 + HC1 = Hg<^ H6 + C 2 H 6 . 

Mercuric Ethochloride. 

These salts are also formed by the direct union of mercury 
and alkyl halogen compounds at ordinary temperatures, 
especially in sunlight, 



Mercuric Ethiodide. 

and by treating di-alkyl mercury compounds with halogens, 
Hg(C 2 H 5 ) 2 + 1 2 = H g < Hs + C 2 H 5 L 



ALKYL COMPOUNDS OP NITROGEN, PHOSPHORUS, ETC. 223 

They interact with moist silver hydroxide, being converted 
into hydroxides, just as sodium iodide, for example, gives 
sodium hydroxide, 



Hg< + AgOH = Hg< + Agl. 

The hydroxides thus formed are thick, caustic liquids, readily 
soluble in water ; they have an alkaline reaction, neutralise 
acids, liberate ammonia from its salts, and precipitate metallic 
hydroxides from their salts. Here, as in the case of com- 
pounds of nitrogen, phosphorus, arsenic, &c., the substitution 
of alkyl groups for hydrogen (or hydroxyl) is accompanied by 
a marked increase in basic properties; mercuric (hydr)oxide 
is a comparatively feeble base. 

Of the other organo-metallic compounds, those of tin, lead, and 
aluminium may be mentioned. Tin and lead form compounds, 
such as Sn(C 2 H 5 )4 and Sn 2 (C 2 H 5 ) 6 , Pb(C 2 H 5 ) 4 and Pb 2 (C 2 H 5 ) 6 , in 
which the metal is tetravalent; stannous ethyl, Sn(C 2 H 5 ) 2 , corre- 
sponding with stannous chloride, is also said to exist. Aluminium 
appears only to give alkyl compounds, such as A1(CH 3 ) 3 and 
A1(C 2 H 5 ) 3 , in which the metal is trivalent. 

The organo-metallic compounds are of great service in 
determining the valency of metals, because, unlike the great 
majority of metallic compounds, most of them vaporise 
without decomposing; by ascertaining experimentally the 
density of the vapour, the molecular weight of the substance 
and the valency of the metal may be established. 



CHAPTEK XIII. 

THE QLYCOLS AND THEIR OXIDATION PRODUCTS. 

It may be assumed as a general rule that the changes 
which any particular group of atoms is capable of under- 
going are largely independent of the nature of the groups 
with which it is combined ; at the same time, however, it 



224 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

must be remembered that the behaviour of every atom or 
group in the molecule is influenced to some extent by that 
of the other atoms or groups, and depends, therefore, on 
the nature of the molecule as a whole. 

As an example, the case of ethane, CH 3 -CH 3 , may be con- 
sidered. This hydrocarbon, as already shown, may be suc- 
cessively transformed into ethyl chloride, CH 3 -CH 2 C1, ethyl 
alcohol, CH 3 -CH 2 .OH, and acetic acid, CH 3 -CO-OH, by 
changes in which only one of the methyl groups takes part, 

CHg ^-H- 3 ^^-3 ^-i} 

CH 3 " ' CH 2 C1 ~ CH 2 -OH T * COOH ' 

it might be supposed, therefore, that by causing the other 
methyl group to undergo the same modifications, compounds 
such as CH 2 C1.CH 2 C1 (ethylene dichloride), CH 2 (OH)-CH 2 .OH 
(dihydroxyethane), and COOH-COOH (oxalic acid) might 
also be obtained, 

CH 3 CH 2 C1 CH 2 -OH COOH 
. CH 3 " " CH 2 C1 " * CH 2 -OH " ' COOH 

Such reactions may, in fact, be brought about, and it is thus 
possible to obtain various series of ^'-substitution products of 
the paraffins, the members of which show, on the whole, a 
close relationship with the corresponding worco-substitution 
products. 

The glycols, or dihydroxy-derivatives of the paraffins, 
discovered by Wiirtz in 1856, afford an example of this 
point ; they form a homologous series of the general formula 
C n H2 M (OH) 2 , and are closely related to the monohydric alcohols. 

Ethylene glycol, or ethylene alcohol, C 2 H 4 (OH) 2 , is the 
simplest glycol, and corresponds with ethyl alcohol, the 
compound, methylene glycol, CH 2 (OH) 2 , which would corre- 
spond with methyl alcohol, being unknown. Ethylene glycol 
is formed in small quantities when ethylene is oxidised with 
a cold, dilute, alkaline solution of potassium permanganate, 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 225 

It is prepared by heating ethylene dibromide, or ethylene 
diehloride, with dilute aqueous alkalies, or alkali carbonates, 
the change which occurs being similar to that which takes 
place in the formation of ethyl alcohol from ethyl chloride, 

C 2 H 4 Br 2 + 2KOH - C 2 H 4 (OH) 2 + 2KBr. 

For this purpose potassium carbonate (138 grains) is dissolved in 
water (1 litre), ethylene dibromide (188 grams) added, and the mix- 
ture boiled in a flask connected with a reflux condenser. As the 
insoluble oily dibromide is converted into ethylene glycol, it passes 
into solution, so that the change is known to be complete when 
globules of oil are no longer visible. The solution is then slowly 
evaporated on a water-bath * to expel most of the water, the semi- 
solid residue mixed with alcohol and ether (which precipitate 
potassium bromide, but dissolve the glycol), and the glycol isolated 
from the filtered solution by fractional distillation. 

Ethylene glycol is a thick, colourless liquid, and has a 
rather sweet taste ; it boils at 197-5, and is miscible with 
water and alcohol in all proportions, but is only sparingly 
soluble in ether. Although it is a neutral substance, it 
dissolves sodium at ordinary temperatures with evolution of 
hydrogen, yielding sodium glycol^ C 2 H 5 2 Na, one atom of the 
metal displacing one atom of hydrogen ; if this substance 
be now heated with sodium, hydrogen is again evolved, and 
disodium glycol, C 2 H 4 2 Na 2 , is formed by a repetition of the 
substitution process. These sodium derivatives, like those 
of the monohydric alcohols, are colourless, crystalline, and 
hygroscopic, and are readily decomposed by water, being re- 
converted into glycol, 

C 2 H 4 2 Na 2 + 2H 2 = C 2 H 6 2 + 2NaOH. 

From its behaviour with sodium it might be assumed that 
glycol contains hydroxyl-groups, and that it gives ^'-substitu- 
tion products (whereas the monohydric alcohols yield only 
mono-substitution products) because it contains two hydroxyl- 

* If the solution be kept in rapid ebullition, a considerable quantity of 
the glycol escapes with the steam. 

Org. O 



226 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

groups. If this were so, it would be expected that giycol, 
like alcohol, would be readily attacked by the chlorides and 
bromides of phosphorus giving rfihalogen compounds ; this is 
indeed the case. When giycol is treated with phosphorus 
pentabromide it is converted into ethylene dibromide, whereas 
with phosphorus pentachloride it yields the dichloride, 

C 2 H 4 (OH) 2 + 2PBr 5 = C 2 H 4 Br 2 + 2POBr 3 + 2HBr. 

Again, it has been shown that ethyl alcohol and other 
hydroxy-compounds interact with acetic anhydride and with 
acetyl chloride, so that if giycol contain two hydroxyl-groups 
it should be converted into a diacetyl-derivative ; this also 
is the fact, since giycol diacetate is readily obtained on heating 
giycol with acetic anhydride, 

C 2 H 4 (OH) 2 + 2(CH 3 .CO) 2 = C 2 H 4 (OCO.CH 3 ) 2 + 2C 2 H 4 2 . 

Giycol diacetate is also formed when ethylene dibromide is 
digested with silver acetate, 

C 2 H 4 Br 2 + 2C 2 H 3 2 Ag = C 2 H 4 (C 2 H 3 2 ) 2 + 2 AgBr ; 

this ester is hydrolysed by boiling alkalies, yielding ethylene 
giycol, which was first obtained by Wlirtz in this way. 

Constitution of Giycol. The facts already stated show 
clearly that giycol contains two hydroxyl-groups; the only 
matter requiring further attention, therefore, is whether these 
two groups are combined with the same or with different 
carbon atoms that is to say, whether giycol has the consti- 
tution CH 3 .CH(OH) 2 or HOCH^CH^OH. This point is 
easily decided on considering the formation of giycol from 
ethylene dibromide; since the latter has the constitution 
CH 2 Br'CH 2 Br, and its conversion into giycol may be regarded 
as a simple process of substitution, giycol may be represented 



by the formula HO-CH 2 -CH 2 .OH or i 2 . This con- 

CH 2 OH 

elusion is confirmed by a study of the behaviour of giycol 
on oxidation and under, other conditions, and of its relations 
to other compounds, 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 227 

Homologties of Ethylene Glycol. The higher glycols, or 
dihydroxy-derivatives of the paraffins, as, for example, 
a/3-propylene glycol, CH 3 -CH(OH)-CH 2 -OH, and ay-butylene 
glycol, CH 3 .CH(OH).CH 2 .CH 2 .OH, are named after the 
tin saturated hydrocarbons of the olefine series, from which 
they may be regarded as derived. As they exist in isomeric 
forms, these are distinguished by employing a, /3, y, &c. to 
denote the positions of the hydroxyl-groups, commencing at 
the terminal carbon atom (compare p. 166). 

The glycols are neutral, thick liquids, similar to ethylene 
glycol in properties ; they are usually prepared by treating 
the olefmes with bromine, and decomposing the dibromo- 
additive products obtained in this way by boiling with alkali 
carbonates (compare also pinacones, p. 141). 

The great advantage of employing constitutional formulae is well 
illustrated by the case of ethylene glycol. From a consideration of 
its method of formation and of one or two simple reactions, it 
is concluded that glycol has the constitution OH.CH 2 .CH 2 .OH. 
Assuming this to be true, its behaviour under given conditions can 
be foretold with tolerable certainty from the facts established in the 
case of ethyl alcohol, because the constitutional formula of a com- 
pound is a summary of its whole chemical behaviour. Ethylene 
glycol contains two -CH 2 -OH groups, each of which is similar to 
that in ethyl alcohol ; it may be supposed, then, that those pro- 
perties of ethyl alcohol which are dependent on the presence of this 
group will also be exhibited by glycol. Since, for example, alcohol 
acts like a metallic hydroxide, and forms salts with one molecule of 
a monobasic acid, ethylene glycol, which contains two hydroxyl- 
groups, should behave as a cfo'acid hydroxide, and form salts with 
two molecules of a monobasic acid. 

When hydrogen chloride is passed into glycol heated at about 
100, ethylene chlorohydrin is formed, 

OH.CH 2 -CH 2 .OH + HC1 = CH 2 C1.CH 2 .OH + H 2 O, 

and when this product is heated with hydrogen chloride at a higher 
temperature, glycol dichloride, or ethylene dichloride, is produced, 



changes which are strictly analogous to the conversion of alcohol 
into ethyl chloride. 



228 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

Again, when ethyl alcohol is carefully oxidised, it is first con- 
verted into aldehyde (the group -CH 2 -OH being transformed into 
-CHO), and then into acetic acid (by the oxidation of the -CHO 
group to -COOH). Since, therefore, glycol contains two -CH 2 -OH 
groups, each of which may undergo these changes, it might be 
foretold that, on oxidation, glycol would probably yield several 
compounds, according as one or both the -CH 2 -OH groups were 
attacked. This also is the fact ; on oxidation with nitric acid 
glycol yields the following compounds, 

CH 2 -OH CH 2 -OH CHO CHO COOH 
CHO COOH CHO COOH COOH 

Glycollic Aldehyde* Glycollic Acid. Glyoxal. Glyoxylic Acid. Oxalic Acid. 

These examples show clearly that, the constitution of any sub- 
stance having been ascertained from a study of some of its 
reactions, its behaviour under given conditions may be foretold 
with tolerable certainty ; for this reason, the general reactions of 
particular groups and the constitutional formulae of organic com- 
pounds are the most important points to bear in mind. 

When an olefine is treated with hypochlorous acid direct com- 
bination ensues, and a chlorohydrin is formed, 

CH 2 :CH 2 + HOC1 = OH-CH 2 .CH 2 C1 

Ethylene. Ethylene Chlorohydrin. 

CH 3 .CH:CH 2 + HOC1 = CH 3 .CHC1.CH 2 .OH. 

Propylene. Propylene Chlorohydrin. 

These chlorohydrins are usually readily acted on by alkalies, 
being converted into oxides by loss of one molecule of hydrogen 
chloride, a change which recalls the conversion of ethyl bromide 
into ethylene, 

CH 2 .OH CH 2 \ 

+KOH= | >0 + KC1 + H 2 0. 
H 2 C1 CHj/ 

Ethylene Oxide. 



I 
C 



CH 2 -OH CH 2 \ 

CHC1 +KOH = CH 2 X +KC1 + H 2 O. 



CH 3 

Propylene Oxide. 

* This, the first oxidation product of glycol, is obtained when glycol 
is oxidised with hydrogen peroxide in presence of a ferrous salt ; other 
glycols and polyhydric alcohols (p. 264) give aldehydes under the same 
conditions. 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 229 

Ethylene oxide is isomeric with aldehyde, C 2 H 4 O ; it is a liquid, 
boils at 13-5, and is slowly decomposed by water, being converted 
into glycol. 

OXIDATION PRODUCTS OF THE GLYCOLS. 

Glyoxal, CHO-CHO, is produced by the oxidation of 
glycol, but it is usually prepared by slowly oxidising alcohol 
or aldehyde with nitric acid, 

CH 3 .CHO + 20 = CHOCHO + H 2 O. 

It is an amorphous substance, readily soluble in alcohol and 
ether ; it shows all the properties of an aldehyde, reduces 
ammoniacal silver nitrate, and combines with sodium 
bisulphite to form a crystalline compound of the composition 
C 2 H 2 2 , 21SraHS0 3 + H 2 0. It also interacts with hydroxyl- 
amine and with phenylhydrazine, giving the compounds 
HON:CH-CH:ISrOH and C 6 H 5 N 2 H:CH-CH:N 2 HC 6 H 5 . 

Hydroxycarboxylic Acids. 

Glycollic acid, OH-CH^COOH, may be obtained by the 
oxidation of glycol, OH-CH 2 'CH 2 'OH, with nitric acid, just 
as acetic acid is produced by the oxidation of alcohol, 
CH 3 'CH 2 -OH, with suitable agents, 

CH 2 -OH CH 2 -OH 



As, however, several other substances are formed, the isolation 
of the acid from the oxidation product is very troublesome. 

It is also formed when amido-acetic acid (glycine, p. 299) 
is treated with nitrous acid, a reaction exactly analogous to 
the conversion of ethylamine into alcohol, 
CH 2 -NH 2 CH 2 -OH 



Glycollic acid is prepared by boiling the potassium salt of 
chloracetic acid with water, when the hydroxyl-group is sub- 
stituted for one atom of chlorine, just as in the formation 
of alcohol from ethyl chloride, 



230 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

CELC1 CH 2 -OH 



The solution is evaporated to dry ness, and the residue extracted 
with acetone, which dissolves the glycollic acid, but not the 
potassium chloride. 

Glycollic acid is a crystalline, hygroscopic substance, and 
melts at 80 ; it is readily soluble in water, alcohol, and 
ether. Assuming that its constitution is correctly represented 
by the formula given above, and of this there can be little 
doubt when its methods of formation are carefully considered, 
it is almost unnecessary to describe at length the chemical 
behaviour of glycollic acid, because this is expressed by its 
constitutional formula. 

Glycollic acid contains one carboxyl-group ; therefore, like 
the fatty acids, it is a monobasic acid, neutralises carbonates, 
and forms salts with metallic hydroxides and with alcohols. 

Glycollic acid also contains one -CH 2 -OH group ; therefore 
it behaves like a primary alcohol, as well as like an acid. 
On oxidation, for example, it yields glyoxylic acid and oxalic 
acid, just as alcohol gives aldehyde and acetic acid, 
CH 2 -OH CHO 

600H + 
CH-OH COOH 



Even when the hydrogen atom of the carboxyl-gronp has 
been displaced, glycollic acid still contains one atom of 
hydrogen, which, like that in alcohols, may be displaced by 
the alkali metals and by the acetyl-group ; ethyl glycollate, 
for example, is readily converted into an acetyl-derivative on 
treatment with acetyl chloride, 

i *' " +CHo-COCl= i 2> ' 3 + HCl. 

COOC 2 H 5 COOC 2 H 5 

Homologues of Glycollic Acid. Glycollic acid may be re- 
garded as hydroxyacetic acid, or acetic acid in which a 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 231 

hydroxyl-group has been substituted for one atom of hydro- 
gen ; as, moreover, other fatty acids yield similar hydroxy- 
derivatives, a homologous series of liydroxycarlioxylic, acids 
may be obtained. 

The more important members of the series are : 

Glycollic acid, or hydroxyacetic acid, OH-CH 2 -COOH. 
Lactic acid, or hydroxypropionic acid, OH-C 2 H 4 -COOH. 

These compounds may also be regarded as oxidation pro- 
ducts of the glycols ; just as glycollic acid is formed on 
oxidising ethylene glycol, so the higher members of the series 
may be obtained from the corresponding glycols by oxidising 
a -CH 2 -OH group to -COOH. 

The lowest member of this series, carbonic acid or hydroxy- 
formic acid, OH COOH, is not known in the free state, since, 
when liberated from its salts, it immediately loses water, and 
is converted into the anhydride, carbon dioxide. 

The third member of the series exists in two isomeric 
forms namely, as a- and ^-hydroxypropionic acid; these 
isomerides are related to propionic acid, in the manner shown 
by the following formulae, 

CH 3 -CH 2 .COOH 

Propionic Acid. 

CH 3 -CH(OH).COOH CH 2 (OH).CH 2 -COOH. 

-Hydroxypropioiiic or Lactic Acid. /3-Hydroxypropionic or Hydracrylic Acid. 

Lactic acid (a-hydroxypropionic acid), CH 3 -CH(OH).COOH, 
is formed during the lactic fermentation of sugars, starch, 
and other substances in presence of nitrogenous animal 
matter, and occurs in sour milk. It can be obtained by 
methods analogous to those given in the case of glycollic 
acid namely, by oxidising a/?-propylene glycol with nitric 
acid, 
CH 3 .CH(OH>CH 2 .OH + 20 = CH 3 -CH(OH).COOH + H 2 ; 

by heating a-chloro- or a-bromo-propionic acid with water, 
dilute aqueous alkalies, or silver hydroxide, 
CH 3 -CHBr.COOH + H 2 = CH 3 .CH(OH)-COOH + HBr ; 



232 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

and by treating a-amido-propionic acid with nitrous acid, 
CH 3 .CH(NH 2 ).COOH + HO-NO = 

CH 3 .CH(OH).COOH + N 2 + H 2 0. 

It is prepared by the lactic fermentation of sugar (see 
butyric acid, p. 158), or simply by heating sucrose or 
glucose with alkalies. Lactic acid is a thick, sour, hygro- 
scopic liquid, miscible with water, alcohol, and ether in all 
proportions; it cannot be distilled, as it undergoes decom- 
position into aldehyde, water, carbon monoxide, and other 
products. When heated with dilute sulphuric acid it is 
decomposed into aldehyde and formic acid, a fact which 
shows that, compared with the fatty acids, lactic acid is 
very unstable, 

CH 3 .CH(OH).COOH = CH 3 -CHO + H-COOH. 
Lactic acid is a monocarboxylic acid, and forms metallic and 
ethereal salts. 

Calcium lactate, (C 3 H 5 O 3 ) 2 Ca + 5H 2 0, and zinc lactate, (C 3 H 5 O 3 ) 2 Zn 
+ 3H 2 O, are crystalline, and readily soluble in hot water. Ethyl 
lactate, CH 3 -CH(OH)-COOC 2 H 5 , is a neutral liquid, but, since 
it contains a ^>CH(OH) group, it yields metallic derivatives 
with potassium and sodium, and, like other hydroxy-compounds, 
it interacts with acetyl chloride, giving ethyl acetyl-lactate, 
CH 3 .CH(O-C 2 H 3 O).COOC 2 H 5 , an ethereal salt of acetyl-lactic 

acid, CH 3 .CH<^ Q C H CH3 . 

Lactic acid also contains the group ^>CH-OH, and shows, 
therefore, most of the reactions of a secondary alcohol. When, 
for example, it is heated with concentrated hydrobromic acid 
it is converted into a-bromo-propionic acid, just as isopropyl 
alcohol gives isopropyl bromide, 

CH 3 .CH(OH>COOH + HBr = CH 3 -CHBr.COOH + H 2 ; 
with concentrated hydriodic acid, however, it yields propionic 
acid, because the a-iodo-propionic acid which is first produced 
is reduced by the excess of hydriodic acid, 

CH 8 .CHLCOOH + HI = CH 3 -CH 2 .COOH + 1 2 . 
On oxidation with potassium permanganate, lactic acid 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 233 

again behaves like a secondary alcohol, and is converted into 
pyruvic acid, just as isopropyl alcohol gives acetone, 
CH 3 .CH(OH)-COOH + = CH 3 .CO-COOH + H 2 0. 

Sarcolactic acid, or paralactic acid, C 3 H 6 O 3 , is the name given 
to the lactic acid which occurs in animals, more especially in the 
muscle juices, and which is best prepared from extract of meat. It 
has the same constitution as lactic acid, because it undergoes the 
same chemical changes, but differs from it in being optically active 
(Part II. p. 545). 

Hydracrylic acid (/3-hydroxypropionic acid), CH 2 (OH)-CH 2 - 
COOH, is not formed during lactic fermentation, but may be 
obtained by reactions exactly similar to those which give 
the corresponding a-acid namely, by oxidising ay-propylene 
glycol, and- by boiling /3-chloro-, bromo-, or iodo-propionic acid, 
CH 2 X-CH 2 -COOH, -with water or weak aqueous alkalies. 

It is a thick, sour syrup, and when heated alone or with 
moderately dilute sulphuric acid, it is converted into acrylic 
acid (p. 263), with loss of the elements of water, a change 
analogous to the conversion of ethyl alcohol into ethylene, 
CH 2 (OH).CH 2 .COOH = CH 2 :CH-COOH + H 2 0. 

In most respects hydracrylic behaves like lactic acid ; it is 
a monocarboxylic acid, but also contains a -CH 2 -OH group, 
so that it shows most of the reactions of a primary alcohol as 
well as those of a monobasic acid ; on oxidation with chromic 
acid, for example, it yields malonic acid, 

CH 2 (OH).CH 2 .COOH + 20 - COOH-CH^COOH + H 2 0. 

Constitutions of the Hydroxypropionic Acids. Since lactic 
acid and hydracrylic acid are both hydroxymonocarboxylic 
acids of the molecular composition C 3 H 6 3 , and only two 
formulae namely, 

CH 8 ..CH(OH).COOH and CH 2 (OH).CH 2 .COOH 

i. ii. 

can be constructed, making the usual assumptions regarding 
valency, all that is necessary is to determine which represents 
the one and which the other acid. This point is, of course, 



234 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

already settled if the constitutions of the chloro-propionic 
or amido-propionic acids be taken as known ; supposing, how- 
ever, this were not the case, the following syntheses of the 
hydroxy-acids establish their constitutions. 

When aldehyde is treated with hydrocyanic acid direct 
combination occurs, and the product is converted into lactic 
acid on boiling it with hydrochloric acid, 

CH 3 .CH(OH)-CN + 2H 2 = CH 3 -CH(OH).COOH + NH 3 . 

Lactic acid, therefore, is represented by formula i., a con- 
clusion which is fully borne out by all other facts. 

When ethylene is treated with an aqueous solution of 
hypochlorous acid, ethylene chlorohydrin is formed (p. 228) ; 
this compound interacts with potassium cyanide in dilute 
alcoholic solution, "giving ethylene cyanohydrin, 

CH 2 (OH).CH 2 C1 + KCN = CH 2 (OH).CH 2 .OT + KC1, 
which, when boiled with mineral acids, is converted into 
hydracrylic acid, 
CH 2 (OH)-CH 2 .CN .+ 2H 2 = CH 2 (OH>CH 2 .COOH + NH 3 . 

Hydracrylic acid, therefore, is represented by formula u. 

Since, moreover, aldehyde and ethylene may be prepared 
from their elements, this is also true as regards the two 
hydroxypropionic acids. 

Lactic acid is sometimes called ethylidenelactic acid, hydracrylic 
acid being named ethylenelactic acid; these names serve to recall 
the facts that lactic acid contains the ethylidene group CH 3 -CH<^, 
hydracrylic acid the ethylene group -CH 2 -CH 2 -. 

Dicarloxylic Acids. 

Glycollic acid, CH 2 (OH)-COOH, being derived from 
ethylene glycol, CH 2 (OH).CH 2 -OH, by the oxidation of 
one of the -CH 2 -OH groups, it might be concluded that the 
other -CH 2 -OH group would be capable of undergoing a 
similar change ; this is found to be so, since on oxidation 
glycollic acid is converted into oxalic -acid, COOILCOOH. 
As, moreover, other glycols, such as ay-propylene glycol, 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 235 

CH 2 (OH)-CH 2 .CH 2 -OH, which contain two -CH 2 -OH groups, 
behave in the same way as ethylene glycol, it is possible to 
prepare a homologous series of dicarboxylic acids of the 
general formula C M H 2n (COOH) 2 . These compounds may also 
be considered as derived from the fatty acids by the substitu- 
tion of the carboxyl-group for one atom of hydrogen, and 
since they contain two such groups, they are dibasic acids. 
The most important members of this series are, 

COOH 

Oxalic, or carboxy formic, acid ........... C 2 H 2 4 or I 

Malonic, or carboxyacetic, acid .......... C 3 H 4 4 or CH 2 

CH 2 -COOH 

Succinic, or /3-carboxypropionic, acid...C 4 H 6 O 4 or I 

CH 2 -uUuH 

f^OOTT 



Isosuccinic, or a-carboxypropionic, acid.C 4 H 6 O 4 or C 

Glutaric acid .................................... C 5 H 8 O 4 

Adipic acid ...................................... C 6 H 10 O 4 

COOH 

Oxalic acid, C 2 H 2 4 , or I , occurs in rhubarb (rheum\ 
COOH 

the dock (rumex), sorrel (oxalis acetosella), and other plants, 
usually in the form of its potassium hydrogen salt, or as 
calcium oxalate; when sorrel is ground up with water, the 
filtered solution gives with calcium chloride a precipitate 
of calcium oxalate. Oxalic acid is formed when alcohol, 
glycol, sucrose, fats, and a great many other organic substances 
are oxidised with nitric acid, and may be obtained by 
numerous reactions, of which the following are the most 
instructive. 

It is formed when sodium is heated at about 350 in 
an atmosphere of carbon dioxide, 



and when sodium or potassium formate is quickly heated 
to about 250, 

2H-COONa = C 2 4 Na 2 + H 2 ; 



236 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

it is also produced, together with many other compounds, 
when an aqueous solution of cyanogen (p. 285) is kept for 
some time, a change which is analogous to the conversion of 
methyl cyanide into acetic acid, 



Ammonium Oxalate. 

Each of these three reactions affords a means of synthesising 
oxalic acid from its elements, since carbon dioxide, formic 
acid, and cyanogen may be obtained from their elements. 

Oxalic acid may be prepared by gently warming sucrose 
(cane-sugar) with about six times its weight of concentrated 
nitric acid. 

The operation is performed in a good draught cupboard, and 
as soon as brown fumes appear the heating is temporarily dis- 
continued, in spite of which oxidation proceeds very vigorously ; 
after some time the solution is evaporated, a little more nitric 
acid being added, if necessary, to ensure complete oxidation. The 
crystals of oxalic acid, which are finally deposited on cooling, 
are separated by filtration through asbestos or glass wool and 
purified by crystallisation from boiling water; further quantities 
may be obtained by evaporating the acid mother-liquors. 

Oxalic acid is prepared on the large scale from sawdust, 
which consists of organic compounds (cellulose, lignin, &c.) 
somewhat similar in composition to sucrose, and which, 
when heated with alkalies, undergo profound decomposition. 

The sawdust is made into a paste with a concentrated solution of 
a mixture of potash (4 parts) and soda (6 parts), and then heated in 
iron pans at about 240 ; afterwards the mass is treated with water, 
the solution of potassium and sodium oxalates boiled with lime, 
the precipitated calcium oxalate washed with water and decomposed 
with dilute sulphuric acid, 

C 2 4 Ca + H 2 SO 4 = C 2 O 4 H 2 + CaSO 4 ; 

the solution of oxalic acid is then filtered from the calcium sulphate 
and evaporated to crystallisation. The acid obtained in this way 
contains small quantities of potassium and sodium hydrogen 
oxalates, from which it is separated only with great difficulty, so 
that on ignition it gives a residue of alkali carbonates ; the pure 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 237 

acid is most conveniently prepared from sucrose. The formation 
of oxalic acid from sawdust and from sucrose cannot be expressed 
by a simple equation ; in both cases a complex molecule containing 
-CH(OH)-CH(OH)- groups undergoes simultaneous decomposition 
and oxidation. 

Oxalic acid crystallises in colourless prisms, which contain 
two molecules of water ; it is readily soluble in alcohol and 
moderately so in water, but only sparingly in ether. When 
quickly heated, it melts at about 100 and loses its water ; the 
anhydrous acid sublimes at about 150, but if heated too 
strongly it decomposes into carbon dioxide and formic acid, 
or its decomposition products, 

C 2 4 H 2 - ILCOOH + C0 2 = H 2 + CO + C0 2 ; 

the anhydrous acid is very hygroscopic, and a powerful 
dehydrating agent. 

Oxalic acid is decomposed by concentrated sulphuric acid, 
but only when heated moderately strongly (distinction from 
formic acid), 



it is a feeble reducing agent, precipitates gold from its solu- 
tions, and is readily oxidised by warm potassium perman- 
ganate (or chlorine water), being converted into carbon dioxide 
and water, a reaction which is employed for the volumetric 
estimation of oxalic acid and also in standardising perman- 
ganate solutions, 



Oxalic acid is dibasic, and forms salts with two equivalents 
of a metallic hydroxide, and with two molecules of a mono- 
hydric alcohol ; it has an acid reaction, decomposes carbonates, 
and dissolves certain metallic oxides. The salts of the alkalies 
are readily soluble in hot water, but most of the other salts 
are sparingly soluble or insoluble. 

Ammonium oxalate, C 2 4 (NH 4 ) 2 + H 2 0, is decomposed, 
giving oxamide, when carefully heated, just as ammonium 
acetate yields acetamide, 



238 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 



when heated with phosphoric anhydride it gives cyanogen 
(p. 285). 

Potassium oxalate, C 2 4 K 2 + H 2 0, is readily soluble in 
water, but potassium hydrogen oxalate, C 2 4 KH, a salt which 
occurs in many plants, is more sparingly soluble ; the latter 
forms with oxalic acid a crystalline compound of the com- 
position C 2 4 KH + C 2 4 H 2 + 2H 2 0, known as ' salts of sorrel,' 
or potassium quadroxalate ; this salt is used in removing iron- 
mould and ink-stains, as it converts the iron into soluble iron 
potassium oxalate. 

Silver oxalate, C 2 4 Ag 2 , is obtained in crystals on adding 
silver nitrate to a neutral solution of an oxalate ; it is only 
sparingly soluble in water, and explodes when quickly heated 
in the dry state, leaving a residue of silver. 

Calcium oxalate, C 2 4 Ca + H 2 0, occurs in crystals in the 
cells of various plants, and is obtained as a white precipi- 
tate on adding a solution of a calcium salt to a neutral or 
ammoniacal solution of an oxalate ; it is insoluble in water, 
and also in acetic acid. 

Oxalic acid and its salts are used to a considerable extent 
in the manufacture of organic dyes, in dyeing, in photography 
(as developers), and in analytical chemistry. The metallic 
salts of oxalic acid are all decomposed by dilute mineral acids, 
yielding oxalic acid, whereas when heated with concentrated 
sulphuric acid they give carbon dioxide, carbon monoxide, 
water, and a sulphate. Oxalic acid and its soluble salts are 
poisonous. The detection of oxalic acid or of an oxalate is 
chiefly based on (a) the behaviour of the neutral solution with 
calcium chloride, and the insolubility of the precipitate in 
acetic acid ; (b) the behaviour of the dry substance when 
heated alone and with sulphuric acid. 

Methyl oxalate, C 2 4 (CH 3 ) 2 , is a colourless, crystalline com- 
pound, melting at 54, and is easily prepared by heating 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 239 

anhydrous oxalic acid with methyl alcohol ; it is readily 
hydrolysed by alkalies and boiling water, and is sometimes 
employed in the preparation of pure methyl alcohol (p. 90). 

Ethyl oxalate, C 2 4 (C 2 H 5 ) 2 , can be obtained in a similar manner ; 
it is a pleasant-smelling liquid, boiling at 186, and sparingly 
soluble in water. It is a curious fact that the methyl salts of 
organic acids are frequently crystalline, even when the ethyl, 
propyl, butyl, &c., salts are liquid at ordinary temperatures. 

The constitution of oxalic acid is determined by its forma- 
tion from glycol, glycollic acid, and formates ; it is a dibasic 
acid because it contains two carboxyl-groups. 

Probably owing to the fact that oxalic acid is very rich 
in oxygen, it is a comparatively unstable compound ; its 
anhydride is unknown, and when treated with phosphorus 
pentachloride, instead of yielding the chloride COC1-COC1, 
as might have been expected, oxalic acid is decomposed into 
water and the oxides of carbon. 

Oxamide, i 2 , is formed as an intermediate product in 



the conversion of cyanogen into ammonium oxalate (p. 286), 
also when ammonium oxalate is heated. It is prepared by 
shaking methyl or ethyl oxalate with concentrated ammonia, 
a method very generally employed in. the preparation of amides 
from ethereal salts (p. 192), 

C 2 4 (C 2 H 5 ) 2 + 2NH 3 = C 2 2 (NHjj) ? + 2C 2 H 5 -OH. 
It is a colourless, crystalline powder, insoluble in water ; when 
heated with water, alkalies, or mineral acids, it is converted 
into oxalic acid or an oxalate, a change exactly analogous to 
that undergone by acetamide (p. 164), 

C 2 2 (NH 2 ) 2 + 2H 2 = C 2 4 H 2 + 2NH 3 . 
Malonic acid, CH 2 (COOH) 2 , the next homologue of oxalic 
acid, has already been mentioned, and the preparation of its 
ethyl salt from chloracetic acid has been described (p. 201). 

If instead of the ethyl salt the free acid be required, the product 
of the action of potassium cyanide on potassium chloracetate is 



240 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

mixed with twice its volume of concentrated hydrochloric acid, and 
the solution saturated with hydrogen chloride ; the clear liquid is 
then decanted from the precipitated potassium chloride, evaporated 
to dryness on a water-bath, and the malonic acid extracted from 
the residue by digesting with ether. 

It was first prepared by oxidising malic acid (p. 245) with 
potassium dichromate ; hence its name. Malonic acid is a 
colourless, crystalline substance, readily soluble in water; it 
melts at 132, and at higher temperatures undergoes decom- 
position into acetic acid and carbon dioxide, 

CH 2 (COOH) 2 = CH 3 .COOH + C0 2 . 

All other dicarboxylic acids, in which both the carboxyl- 
groups are united to one and the same carbon atom, are 
decomposed in a similar manner under the influence of heat. 

Succinic acid, C 4 H 6 4 , or CHg-COOH^ occurg ^ ambe ^ 

CH 2 .COOH 

and also in smaller quantities in lignite (fossil-wood), in 
many plants, and in certain animal secretions. It is formed 
during the alcoholic fermentation of sugar, and in several 
other fermentation processes; also when fats are oxidised 
with nitric acid. 

It can be obtained from its elements in the following 
manner : acetylene, which can be prepared from carbon and 
hydrogen, is reduced to ethylene, the latter passed into 
bromine, and the ethylene dibromide thus produced boiled 
with potassium cyanide in aqueous alcoholic solution, when 
ethylene dicyanide is formed, 

C 2 H 4 Br 2 + 2KCN = C 2 H 4 (CN) 2 + 2KBr ; 
this compound is decomposed by boiling it with alkalies or 
mineral acids, succinic acid and ammonia being obtained 
(compare foot-note, p. 146), 



2 .COOH 



It may also be prepared synthetically from ethyl acetoacetate (or 
ethyl malonate) and ethyl chloracetate, 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 241 



2 Cl.COOC 2 H 5 =CH 3 .CO.CH.CH 2 .COOC 2 H 5 

COOC 2 H 5 COOC 2 H 5 + NaCl 

CH 3 .CQ.CH.CH 2 .COOC 2 H 5 

+ 3KOH = 
COOC 2 H 5 

CH 2 .CH 2 .COOK 

(Acid Hydrolysis, p. 197). I + CHg-COOK + 2C 2 H 5 .OH. 

COOK 



Succinic acid is usually prepared by distilling amber from 
iron retorts ; the dark-brown oily distillate is evaporated, and 
the dirty-brown crystalline residue of succinic acid purified by 
recrystallisation from hot dilute nitric acid. 

Succinic acid crystallises in colourless prisms, melts at 185, 
and sublimes readily ; it has an acid, unpleasant taste, and is 
only sparingly soluble in cold water, alcohol, and ether. It 
is a dibasic acid, and its salts, the succinates, with the 
exception of those of the alkalies, are sparingly soluble or 
insoluble in water. 

Ammonium succinate, C 4 H 4 4 (NH 4 ) 2 , is sometimes employed 
in the separation of iron from manganese, as, on adding a 
solution of a ferric salt to ammonium succinate, the whole of 
the iron is converted into an insoluble basic salt, which is 
obtained as a buff precipitate. 

The constitution of succinic acid is determined by its forma- 
tion from ethylene dibromide, and by the fact that the only 
alternative formula for a dicarboxylic acid of the molecular 
composition C 4 H 6 4 must be assigned to isosuccinic acid (see 
below). 



Succinic anhydride, i 2 >0. is formed when succinic 

CH 2 .CO X 

acid is distilled, C 4 H 6 4 = C 4 H 4 3 + H 2 0, but a large pro- 
portion of the acid passes over unchanged. It is prepared 
by heating the acid with phosphorus oxy chloride for some 
time and then distilling, the oxychloride combining with the 
water which is produced, and thus preventing the reconver- 
sion of the anhydride into the acid; phosphorus pentoxide, 

or*. P 



242 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

acetyl chloride, or some other dehydrating agent may be used 
in the place of the oxychloride. 

Succinic anhydride is a colourless, crystalline substance, and 
melts at 120; it resembles the anhydrides of the fatty acids 
in chemical properties, and when boiled with water or alkalies 
it is reconverted into succinic acid or a succinate. 

Succinic anhydride differs from the anhydrides of fatty 
acids in this, that it is formed from one molecule of the acid 
with elimination of one molecule of water, whereas the anhy- 
dride of a fatty acid is produced from two molecules of the 
acid in a similar manner, 

CH 2 -COOH CH 2 -C 



CH 2 -CCK 
CH,COOHCH,CO >0 + 



CHg-COOH 



the constitution of succinic anhydride is therefore expressed 
by the above formula, which recalls the fact that both the 
carboxyl-groups take part in the change, as is shown by the 
neutral character of the anhydride. Many other dicarboxylic 
acids are converted into their anhydrides in a similar manner. 



CH 2 .COC1 

Succinyl chloride. \ , is formed when succinic acid is 

CH 2 .COC1 

treated with two molecules of phosphorus pentachloride,* the inter- 
action recalling that which occurs in the formation of acetyl 
chloride, 

CH 2 -COOH CH 2 .COC1 

+ 2PCL= I + 2POCL+2HC1. 

CH 2 .COOH CH 2 -COC1 

It is a colourless liquid, boils at 190, and resembles acetyl chloride 
in chemical properties ; like the latter, it is decomposed by water, 
alkalies, and hydroxy-compounds, yielding succinic acid or a 
succinate. 

* The product is probably a mixture of succinyl chloride and a di- 
chloro-substitution derivative of succinic anhydride of the constitution 
CH 2 -CC1 2 \ 
I >0, 

CH 2 -CO ' 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 243 

CH 2 .CONH 2 

Succinamide, \ , is prepared by shaking ethyl suc- 

CH 2 -CO'NH 2 

cinate with concentrated ammonia ; it is a crystalline substance, 
melts at 242-243, and is only very sparingly soluble in cold water. 
When heated with water it is slowly converted into ammonium 
succinate, just as oxamide is converted into ammonium oxalate, 

CH 2 .CO-NH 2 CH 2 .COONH 4 

I + 2H 2 = I 

CH 2 .CO-NH 2 CH 2 .COONH 4 . 

Succinamide cannot be obtained by distilling ammonium succinate, 
although oxamide and acetamide are produced by the distillation 
of the corresponding ammonium salts; this fact shows that it 
is not always safe to judge by analogy, since compounds very 
closely related in constitution may, in certain respects, behave very 
differently. When, in fact, ammonium succinate or Succinamide 
is heated, it is converted into succinimide. 

CH 2 -CO\ 
Succinimide, I /NH, is also formed when succinic anhy- 

CH 2 -CO 

dride is heated in a stream of dry ammonia ; it is readily soluble in 
water, from which it crystallises with one molecule of water, the 
anhydrous substance melting at 126. When boiled with water, 
alkalies, or mineral acids, it is converted into succinic acid, 

CH 2 .CO\ CH 2 -COOH 

I >NH + 2H 2 0= I +NH 3 . 

CH 2 .CCr CH 2 .COOH 

The constitution of succinimide, as expressed by the above formula, 
is based principally on its methods of formation ; it may be regarded 
as a di-substitution product of ammonia that is to say, as ammonia 
in which two atoms of hydrogen have been displaced by the 

CH 2 -CO- 
divalent succinyl-group I , just as an amide is a mono- 

CH 2 -CO- 

substitution product of ammonia. Many other dicarboxylic acids 
yield imides similar in constitution to succinimide. 

Although succinimide is not an acid in the ordinary sense of the 
word, has a neutral reaction, and does not decompose carbonates, 
it contains one atom of hydrogen displaceable by metals. When, 
for example, a solution of potash in alcohol is added to an alcoholic 
solution of succinimide, a crystalline derivative, potassium succin- 

CH 2 .CO\ 
imide, \ )*NK, is produced ; this compound interacts with 



CH 2 - 



CO 



244 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

silver nitrate, giving silver succinimide, and the latter, on treatment 
with ethyl iodide, yields ethyl succinimide, 



It has already been pointed out that hydrogen in combination 
with carbon becomes displaceable by metals when the carbon atom 
is directly united with two >CO groups, as in ethyl acetoacetate 
and ethyl malonate. From the behaviour of succinimide, and of 
other imides, it is found that the hydrogen atom of an imido- 
group >NH is also displaceable by metals when the imido-group 
is directly united with two >CO groups. 

Isosuccinic acid, CH 3 -CH(COOH) 2 , is isomeric with succinic acid ; 
it may be prepared by treating an alcoholic solution of the sodium 
derivative of ethyl malonate with methyl iodide, and hydrolysing 
the product, a reaction which shows that isosuccinic acid is methyl- 
malonic acid, 

CHNa(COOC 2 H 5 ) 2 + CH 3 I = CH 3 .CH(COOC 2 H 5 ) 2 + Nal. 

It is a crystalline substance, sublimes readily, and melts at 130 ; 
it does not form an anhydride, and when heated alone, or with 
water, it is decomposed into propionic acid and carbon dioxide, 
just as malonic acid gives acetic acid and carbon dioxide, 

CH 3 .CH(COOH) 2 =CH 3 .CH 2 .COOH + CO., 

The higher members of this series of dicarboxylic acids exist in 
several isomeric forms ; four acids of the composition C 5 H 8 O 4 , for 
example, are theoretically possible, and four are actually known 
namely, 

CH 3 .CH.COOH 
CH 2 .COOH 

Normal Glutaric Acid. Pyrotartaric Acid or 

Metliylsuccinic Acid. 

COOH 



Ethylmalonic Acid. Dirnethylmalonic Acid. 

Adipic acid, C 6 H 10 O 4 , is of some importance, and is often obtained 
on oxidising fats with nitric acid ; it may be produced synthetically 
by heating j8-iodo- propionic acid with finely divided silver, the 
reaction being analogous to the production of ethane by the action 
of sodium or zinc on methyl iodide, 

2CH 2 I.CH 2 .COOH + 2 Ag = COOH .[CH^-COOH + 2AgI j 
it is a crystalline substance, melting at 148, 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 245 

Hydroxydicarboxylic Acids. 

With the exception of oxalic acid, the dicarboxylic acids just 
considered are capable of yielding substitution products in exactly 
the same way as the fatty acids ; malonic acid, for example, 
may be converted into chloromalonic acid, CHC1(COOH) 2 , 
hydroxymalonic acid, HO'CH(COOH) 2 , &c. ; succinic acid 
into bromosuccinic acid, COOH-CHBr-CH 2 -COOH, dibromo- 
succinic acid, COOH-CHBr-CHBr-COOH, hydroxysuccinic 
acid, COOH-CH(OH).CH 2 .COOH, dihydroxysuccinic acid, 
COOH.CH(OH).CH(OH)-COOH, and so on. Some of these 
compounds namely, the hydroxy-derivatives occur in nature, 
and for this and other reasons are of considerable importance. 

CH(OH)-COOH 

Malic acid, i or C 4 H fi 5 , a rnonohydroxy- 

CH 2 .COOH 

derivative of succinic acid, occurs, not only in the free state, 
but also in the form of salts, in many plants, more especially 
in (unripe) apples, from which it derives its name (acidum 
mdlicum), in grapes, and in the berries of the mountain ash. 
It may be obtained by boiling bromosuccinic acid with water 
and silver hydroxide, a reaction analogous to the formation 
of lactic acid from a-bromo-propionic acid, 

CHBr-COOH CH(OH)-COOH 

i + Ag-OH = i v ' +AgBr. 

CH 2 .COOH CH 2 -COOH 

As, therefore, bromosuccinic acid is easily prepared by 
brominating succinic acid (p. 166), and succinic acid may be 
synthesised in the manner already described (p. 240), it is 
possible to obtain malic acid from its elements. 

Malic acid is produced on treating amidosuccinic acid, or 
aspartic acid (a compound which may be obtained indirectly 
from asparagus*), with nitrous acid, just as lactic acid may 
be prepared from a-amido-propionic acid, 

* Asparayin, COOH'CH(NH 2 )'CH 2 'CO'NH 2 , the amide of aspartic acid, 
occurs in asparagus ; when boiled with acids or alkalies it is converted into 
aspai-tic acid, COOH.CH(NH) fl .CH a .COOH. 



246 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

+ 



= 
CH 2 .COOH CH 2 -COOH 

It is usually prepared from the juice of unripe berries of the 
mountain ash. 

The expressed juice is boiled with milk of lime and the crystal- 
line, sparingly soluble calcium salt, C 4 H 4 O 5 Ca + H 2 0, which is 
precipitated, dissolved in hot dilute nitric acid ; the calcium 
hydrogen malate, (C 4 H 5 5 ) 2 Ca + 6H 2 O J which separates in crystals, 
is then decomposed with the theoretical quantity of oxalic acid, 
and the filtered solution evaporated. 

Malic acid is a crystalline, deliquescent substance, melts at 
100, and is readily soluble in water and alcohol, but only 
sparingly in ether ; its metallic and ethereal salts are of little 
importance. 

Many of the reactions of malic acid may be foretold from 
a consideration of its constitution, which is established by its 
methods of formation. Since, for example, it is a hydroxy- 
derivative of succinic acid, it is to be expected that, on 
reduction with hydriodic acid at a high temperature, it will be 
converted into succinic acid, just as lactic acid is converted 
into propionic acid ; also that, when heated with hydrobromic 
acid, it will yield bromosuccinic acid, a change which would 
be analogous to the conversion of lactic into bromopropionic 
acid. Both these changes actually take place, 
COOH.CH(OH).CH 2 -COOH + 2HI = 

COOH.CH 2 .CH 2 .COOH + H 2 + 1 2 
COOH.CH(OH).CH 2 -COOH + HBr = 

COOH-CHBr-CHg-COOH + H 2 0. 

Although the malic acid obtained from plants undergoes 
exactly the same chemical changes as that prepared from 
bromosuccinic acid, the two acids are not identical in all 
respects; they differ principally in their action on polarised 
light, the naturally occurring acid being optically active 
(Part II. p. 545). 

When malic acid is heated for a long time at 130 it does not 
form malic anhydride, as might have been expected from the 



+ H 2 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 247 

behaviour of succinic acid, but is slowly converted into fumaric 
acid and water, 

CH(OH).COOH CH-COOH 

CH 2 .COOH CH.COOH 

if now the fumaric acid be distilled, part passes over unchanged, 
the rest being converted into maleic anhydride and water, 
CH.COOH CH-COOHx 
II =11 >0 + H 2 0. 

CH-COOH CH-eOOH x 

Maleic anhydride is decomposed by boiling water, giving maleic 
acid, which has the same constitution as fumaric acid that is to 
say, both compounds are unsaturated dicarboxylic acids of the 
constitution COOH-CH:CH-COOH ; the existence of these two 
isomerides, and other cases of isomerism of a similar kind, are 
accounted for by the theory of stereochemical isomerism proposed 
by van't Hoff and Wislicenus (Part II. p. 558). 

Tartaric acid, or dihydroxy succinic acid, C 4 H 6 6 or 

CH(OH>COOH 

i , is one of the most commonly occurring 

CH(OH)-COOH 

vegetable acids, and is contained in grapes, in the berries of 
the mountain ash, and in other fruits ; during the later stages 
of the fermentation of grape-juice a considerable quantity of 
' argol,' or impure potassium hydrogen tartrate, is deposited, 
and it is from this salt that the tartaric acid of commerce is 
obtained. 

Tartaric acid can be obtained from succinic acid, and, 
therefore, from its elements, by reactions similar to those 
employed in the synthesis of malic acid ; dibromosuccinic acid 
is first prepared by strongly heating succinic acid with bromine 
and amorphous phosphorus (p. 166), and two hydroxyl- 
groups are then substituted for the two atoms of bromine in 
the usual way namely, by heating the dibromo-derivative 
with water and silver hydroxide,* 

CHBr-COOH CH(OH)-COOH 

+ 2Ag-OH = i v + 2AgBr. 

CHBr-COOH CH(OH)-COOH 

* The tartaric acid obtained in this way is optically inactive, and is ft 
inixture of racemic acid and mesotartaric acid (p. 251). 



248 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

Tartaric acid may also be obtained synthetically from glyoxal 
(p. 229), which, like other aldehydes, combines directly with 
hydrogen cyanide, 



+ =; 

CHO CH(OH)-CN 

the dicyanohydrin thus produced is decomposed by mineral 
acids, giving tartaric acid,* just as cyanoacetic acid yields 
malonic acid, 

CH(OH). CN CH(OH).COOH 

CH(OH).CN CH(OH)-COOH 

Tartaric acid is prepared on the large scale from argol. This 
crude, coloured deposit is partially purified by recrystallisation 
from hot water, and its aqueous solution is then boiled with 
chalk, when insoluble calcium tartrate is precipitated, neutral 
potassium tartrate remaining in solution, 
2C 4 H 5 6 K + CaC0 3 = C 4 H 4 6 Ca + C 4 H 4 6 K 2 + C0 2 + H 2 ; 

the calcium salt is separated, and the solution treated with 
calcium chloride, when a second precipitate of calcium tartrate 
is obtained, 

C 4 H 4 6 K 2 + CaCl 2 = C 4 H 4 6 Ca + 2KC1. 

The calcium tartrate from these two operations is washed 
with water, and decomposed with the theoretical quantity of 
dilute sulphuric acid; finally, the filtered solution of the 
tartaric acid is evaporated to crystallisation. 

Tartaric acid forms large transparent crystals, and is readily 
soluble in water and alcohol, but insoluble in ether ; it melts 
at about 167, but not sharply, owing to decomposition taking 
place. When heated for a long time at about 150, it is con- 
verted into tartaric anhydride, C 4 H 4 5 , and several other 
compounds, and on dry distillation it yields a variety of pro- 
ducts, among others, pyruvic acid and pyrotartaric acid. 

Tartaric acid, like other dicarboxylic acids, forms both 

* This acid is also optically inactive, and is said to consist of racemic 
acid (p. 251). 



THE GLYCOLB AND THEIR OXIDATION PRODUCTS. 249 

normal and hydrogen salts, some of which are of considerable 
importance. 

Normal potassium tartrate, C 4 H 4 6 K 2 + JH 2 0, is readily 
prepared by neutralising the acid, or the acid potassium salt, 
with potash; it is readily soluble in cold water, in which 
respect it differs from potassium hydrogen tartrate, C 4 H 5 6 K, 
which is only sparingly soluble. The latter is precipitated* 
on adding excess of tartaric acid to a concentrated neutral 
solution of a potassium salt (test for potassium), and also on 
treating an aqueous solution of normal potassium tartrate with 
one equivalent of a mineral acid, 

C 4 H 4 6 K 2 + HC1 = C 4 H 5 6 K + KC1 ; 

it is known in commerce as ' argol ' or ' cream of tartar.' 

Potassium sodium tartrate, or ' Eochelle salt,' C 4 H 4 6 KNa 
+ 4H 2 0, is obtained when potassium hydrogen tartrate is 
neutralised with sodium carbonate, and then concentrated ; 
it forms large transparent crystals, and is employed in the 
preparation of Fehling's solution (p. 268). 

Calcium tartrate, C 4 H 4 6 Ca + 4H 2 0, being insoluble in 
water, is precipitated on adding a soluble calcium salt to a 
neutral solution of a tartrate ; it is readily soluble in potash, 
but is reprecipitated on boiling the solution, a behaviour 
which is made use of in testing for tartaric acid. 
Tartar emetic, or potassium antimonyl tartrate, 
C 4 H 4 6 K(SbO) + JH 2 0, 

is prepared by boiling potassium hydrogen tartrate with 
antimonious oxide and water; it is readily soluble in 
water, and is used in medicine, as an emetic, and in dyeing, 
as a mordant. 

The detection of tartaric acid or of a tartrate is based (a) 
on the behaviour of the neutral solution with calcium chloride 
(in the cold), and on the solubility of the precipitate in 
potash ; (b) on the behaviour of the neutral solution with an 
ammoniacal solution of silver nitrate, from which a mirror 
* The precipitation is hastened by stirring with a glass rod. 



250 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

of silver is deposited on warming; (c) on the fact that the 
solid compound rapidly chars when heated alone, giving an 
odour of burnt sugar ; it also chars when heated with con- 
centrated sulphuric acid, sulphur dioxide and the two oxides 
of carbon being evolved. 

That the constitution of tartaric acid is expressed by the 
formula given above is shown by the methods of formation 
of the acid; it is a dihydroxy-derivative of succinic acid, 
just as malic acid is a monohydroxy-derivative of the same 
compound. 

On reduction with hydriodic acid, tartaric acid is converted 
first into malic, then into succinic acid, 



+ 2H[= + 

CH(OH>COOH CH 2 .COOH 



2 

+ = COOH 
CH(OH)-COOH CH 2 -COOH 

whereas when heated with concentrated hydrobromic acid it 
yields dibromosuccinic acid, as was to be expected, 

CH(OH).COOH = CHB,COOH 

CH(OH).COOH CHBr-COOH 

It is a remarkable fact that four distinct modifications of 
tartaric acid are known namely, dextrotartaric acid (the 
compound just described), levotartaric acid, racemic acid, and 
mesotartaric acid. These four compounds have the same con- 
stitution that is to say, they are all dihydroxy-derivatives of 
succinic acid, as represented by the formula, 

COOH-CH(OH).CH(OH).COOH ; 

they differ, however, in certain physical properties, as, for 
example, in crystalline form, solubility, &c., but more 
especially in their behaviour towards polarised light ; com- 
pounds which show a relationship of this kind are called 
optical isomerides (Part II. p. 541). The salts of the acids- 
also exhibit differences of this kind. 



THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 251 

Dextrotartaric acid rotates the plane of polarisation to the right, 
levotartaric acid to an equal extent to the left. 

Racemic acid is optically inactive ; it is produced when equal 
quantities of the dextro- and levo-acids are dissolved in water, and 
the solution of the mixture allowed to crystallise. It may be 
obtained synthetically by heating an aqueous solution of dibromo- 
succinic acid with silver hydroxide, as described above ; also from 
glyoxal. Racemic acid may be resolved into dextro- and levo- 
tartaric acids (Part II. pp. 542, 557). 

Mesotartaric acid, like racemic acid, is optically inactive, but it 
cannot be resolved into the two optically active modifications ; it 
is formed, together with racemic acid, when dextrotartaric acid is 
heated for a long time with a small quantity of water at about 165, 
and when dibromosuccinic acid is heated with silver hydroxide. 

Hydroxytricarboxylic A cids. 

Citric Acid, CgHgO^, like tartaric acid, occurs in the free 
state in the juice of many fruits ; it is found in com- 
paratively large quantities in lemons, in smaller quantities 
in currants, gooseberries, raspberries, and other sour fruit. 
It is prepared on the large scale from lemon-juice, which is 
first boiled, in order to coagulate and precipitate albuminoid 
matter, and then neutralised with calcium carbonate ; the cal- 
cium salt, which is precipitated from the hot solution, is washed 
with water, decomposed with the theoretical quantity of dilute 
sulphuric acid, and the filtrate from the calcium sulphate 
evaporated to crystallisation. 

It is also prepared by fermenting glucose solutions with 
citromycetes. 

Citric acid forms large transparent crystals which contain 
one molecule of water and melt at 100, but do not lose 
their water until about 130; it is readily soluble in water 
and fairly so in alcohol, but insoluble in ether. Like tartaric 
acid, and several other organic acids, it has the property of 
preventing the precipitation of certain metallic hydroxides 
from solutions of their salts. Solutions of ferric chloride and of 
zinc sulphate, for example, give no precipitate with potash or 
ammonia if citric acid be present ; on account of this property, 



252 THE GLYCOLS AND THEIR OXIDATION PRODUCTS. 

citric acid and tartaric acid are employed in analytical 
chemistry and in calico-printing. 

Citric acid is a tricarboxylic acid, and, like phosphoric 
acid, forms three classes of salts, as, for example, the three 
potassium salts, C 6 H 5 7 K 3 , C 6 H 6 7 K 2 , and C 6 H 7 7 K, all 
of which are readily soluble in water. Calcium citrate, 
(C 6 H 5 7 ) 2 Ca 3 + 4H 2 0, is not precipitated on adding a solu- 
tion of a calcium salt to a neutral solution of a citrate, 
because it is readily soluble in cold water; on heating, 
however, a crystalline precipitate is produced, as the salt 
is less soluble in hot than in cold water. This behaviour, 
and the fact that the precipitate is insoluble in potash, 
distinguishes citric from tartaric acid. When heated alone 
citric acid chars and gives irritating vapours, but no 
smell of burnt sugar is noticed ; it also differs from tartaric 
acid, inasmuch as it does not char when gently heated with 
concentrated sulphuric acid until after some time. 

Citric acid may be obtained synthetically by a series of 
reactions which show it to be a hydroxytricarboxylic acid of 
the constitution, 

CH 2 -COOH 



(OH)-COOH. 
CH 2 -COOH 

Symmetrical dichloracetone, CH 2 C1-CO-CH 2 C1, which may be 
obtained by oxidising aa-dichlorohydrin (p. 257) with chromic acid, 
like other ketones, combines with hydrogen cyanide, forming 

OTT 

the cyanohydrin, (CH 2 Cl) 2 C<^p,,, ; this product, like other com- 
pounds containing the -CN group, is converted into a carboxylic 

OTT 
acid, (CH 2 C1) 2 C<~QQ,T, by boiling mineral acids. The two atoms 

of chlorine in this acid may now be displaced by -CN groups by 
digesting the potassium salt of the acid with potassium cyanide, 

CH 2 C1 CH 2 -CN 

C(OH)-COOK + 2KCN = C(OH)-COOK + 2KC1, 
CH a -CN 



THE GLTCOLS AND THEIR OXIDATION PRODUCTS. 253 

and this dicyano-derivative may then be converted into citrio acid 
by boiling it with hydrochloric acid, 

CH 2 CN CH 2 COOH 

C(OH)-COOH + 4H 2 = C(OH)-COOH +2NH 3 . 
CH 2 -CN CH 2 -COOH 

This view of the constitution of citric acid is borne out by all the 
reactions of the compound ; it is shown to contain one hydroxyl- 
group by the fact that ethyl citrate, C 3 H 4 (OH)(COOC 2 H 5 ) 3 , yields 
a monacetyl-derivative with acetyl chloride. When heated alone 
at 175, citric acid is converted into aconitic acid, just as malic is 
converted into fumaric acid, 

CH 2 -COOH CHCOOH 
C(OH)-COOH = C-COOH + H 2 O ; 
CH 2 COOH CH 2 COOH 

when carefully warmed with sulphuric acid it yields acetone- 
dicarboxylic acid, with evolution of carbon monoxide, 

CH 2 -COOH CH 2 -COOH 
C(OH)-COOH = CO + CO + H 2 O, 
CH 2 -COOH CH 2 -COOH 

and on reduction with hydriodic acid it is converted into 
CH 2 COOH 

tricarballylic acid, CH-COOH. 
CH 2 COOH 



CHAPTEK XIV. 

TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 

In the preceding chapter it has been shown that it is 
possible to convert a paraffin first into a monohydric alcohol, 
and then into a dihydric alcohol, or glycol, by the substitution 
of hydroxyl-groups for atoms of hydrogen ; ethane, for example, 



254 TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 

may be converted into ethyl alcohol and ethylene glycol, 
propane into propyl alcohol and propylene glycol. 

In a similar manner those paraffins containing three or more 
carbon atoms may be converted into trihydric alcohols, com- 
pounds which stand in the same relation to the glycols as the 
latter to the monohydric alcohols, 

Propyl Alcohol. Propylene Alcohol. 

CH 3 .CH 2 .CH 2 .OH CH 3 .CH(OH).CH 2 .OH 

Propenyl Alcohol. 

CH 2 (OH).CH(OH).CH 2 .OH. 

As, however, the preparation of such trihydric alcohols from 
the paraffins is a matter of very considerable difficulty, their 
study has necessarily been very limited except in the case of 
glycerol, which, from its occurrence in such large quantities in 
natural fats and oils, has offered exceptional opportunities for 
investigation. 

Glycerol, glycerin, propenyl alcohol, or trihydroxypropane, 
C 3 H 5 (OH) 3 , or CH 2 (OH).CH(OH).CH 2 .OH, has been pre- 
viously referred to as one of the unimportant products of 
the alcoholic fermentation of sugar, and its preparation from 
fats and oils, which consist essentially of tripalmitin, 
tristearin, and triolein (esters of which glycerol is the base) 
has been described. 

The concentrated glycerol obtained on evaporating its 
aqueous solution (p. 173) may be further purified and freed 
from water by distillation under reduced pressure, the first 
fractions, which contain the water, being collected separately. 

Glycerol may be obtained from its elements by the following 
series of reactions : Acetylene, obtained by Berthelot's synthetical 
method or from calcium carbide, is converted into acetaldehyde 
(p. 84), and the latter is oxidised to acetic acid, from which 
acetone is prepared in the usual manner (p. 130) ; this ketone 
is first converted into isopropyl alcohol (p. 131) and then into 
propylene (p. 106) ; this olefine unites directly with bromine, 
yielding propylene dibromide, and from the latter, by heating 
with bromine in presence of iron (Part II. p. 352), propenyl 
tribromide, CH 2 Br CHBr-CH g Br ? is obtained, The three bromine 



TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 255 

atoms in this compound are next displaced by acetyl -groups 
by digesting with silver acetate (p. 226), and the product, pro- 
penyl or glyceryl acetate, is hydrolysed with aqueous or alcoholic 
potash. The complete synthesis of glycerol may be summarised 
as follows, 

C 2 H 2 -*CH 3 .CHO CH 3 -COOH CH 3 .CO.CH 3 ^CH 3 .CH(OH)-CH3 

-^CH 3 -CH:CH 2 ^CH 3 -CHBr-CH 2 Br *CH 2 Br-CHBr-CH 2 Br 
>CH 2 (OAc).CH(OAc)-CH 2 -OAc* >CH 2 (OH).CH(OH).CH 2 -OH. 

Pure glycerol is a colourless, crystalline substance, melting 
at 17; as ordinarily prepared, however, it is a thick syrup 
of sp. gr. 1-265 at 15, and does not solidify readily owing to 
the presence of water and traces of other impurities. It boils 
at 290 under ordinary atmospheric pressure, without decom- 
posing ; if, however, it contain even traces of salts it under- 
goes slight decomposition, so that in such cases it must first 
be distilled in a current of superheated steam. Glycerol is 
very hygroscopic, and rapidly absorbs water from the air, 
mixing with it and also with alcohol in all proportions ; it is 
insoluble in ether, a property which is common to most 
substances that contain many hydroxyl-groups. It has a 
distinctly sweet taste ; this property also seems to be con- 
nected with the presence of hydroxyl-groups, as is shown by 
the fact that other trihydric alcohols, and to an even greater 
extent the tetra-, penta-, and hexa-hydric alcohols, are sweet, 
sugar-like compounds. 

Glycerol readily undergoes decomposition into acrolein 
(p. 262) and water, 

C 3 H 5 (OH) 3 = C 3 H 4 + 2H 2 ; 

this change takes place to a slight extent when impure 
glycerol is distilled, but much more readily and completely 
when glycerol is heated with potassium hydrogen sulphate, 
phosphorus pentoxide, or other dehydrating agents. 

Glycerol, like glycol, yields a variety of oxidation products 
according to the conditions under which it is treated ; when 
carefully oxidised with dilute nitric acid it is converted into 

* CH 3 -CO - is represented by Ac in this formula. 



256 TRIHYDRIC AND POLYHYDRIO ALCOHOLS. 

glyceric acid, a change analogous to the formation of glycollic 
acid from glycol, 

CH 2 (OH).CH(OH).CH 2 .OH + 20 = 

CH 2 (OH).CH(OH).COOH + H 2 ; 

under other conditions, however, it is usually oxidised to a 
mixture of glycollic, oxalic, and carbonic acids, 

CH 2 (OH).CH(OH)-CH 2 .OH + 40 = 

CH 2 (OH)-COOH + C0 2 + 2H 2 
CH 2 (OH).CH(OH>CH 2 .OH + 60 = 

COOH-COOH + C0 2 + 3H 2 0. 

Glycerol is extensively used in the preparation of nitro- 
glycerin (p. 258) and toilet-soaps, also for filling gas-meters ; 
it is used in smaller quantities in medicine and as an anti- 
putrescent in preserving food materials. 

Derivatives of Glycerol. Knowing from its synthesis that 
glycerol is a trihydric alcohol of the constitution given above, 
its behaviour under various conditions may be foretold with a 
good prospect of success, if that of ethyl alcohol and of glycol 
be borne in mind. The fact, for example, that glycerol 
contains hydrogen, displaceable by sodium, was only to be 
expected, and, just as in the case of glycol, only one atom of 
hydrogen is displaced at ordinary temperatures ; the product, 
C 3 H 5 (OH) 2 'ONa, is hygroscopic, and is immediately decom- 
posed by water. 

Again, the behaviour of glycerol with acids is analogous to 
that of alcohol and of glycol ; when heated with acetic acid, 
for example, it yields the ester triacetin, or glyceryl acetate, 
and water, 

C 3 H 5 (OH) 3 + 3CH 3 .COOH = C 3 H 5 (0-CO.CH 3 ) 3 + 3H 2 0. 

It is obvious, however, that triacetin is not the only ester 
which may be produced by the interaction of glycerol and 
acetic acid, because, being a triacid base, glycerol may yield 
compounds, such as monacetin and diacetin, by the displace- 
ment of only one, or of two, atoms of hydrogen, 



TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 257 

C 3 H 5 (OH) 3 + CHg-COOH = C 3 H 5 (OH) 2 .O.CO-CH 3 + H 2 
C 3 H 5 (OH) 3 + 2CH 3 .COOH = C 3 H 6 (0-CO.CH 3 ) 2 .OH + 2H 2 0. 
These three compounds may all be prepared by heating 
glycerol with acetic acid, the higher the temperature and 
the larger the relative quantity of acetic acid employed, the 
larger the proportion of triacetin produced. Acetic anhydride 
acts more readily than acetic acid, but gives the same three 
products. 

Chlorohydrins. The action of concentrated hydrochloric 
acid on glycerol is similar to that of acetic acid ; at moderately 
high temperatures, and employing only the theoretical quantity 
of the acid, one atom of chlorine is substituted for one 
hydroxyl-group, and (property!) cliloroliydrin * is formed, just 
as ethylene glycol is converted into ethylene chlorohydrin, 

C 3 H 5 (OH) 3 + HC1 = C 3 H 5 C1(OH) 2 + H 2 ; 
with excess of hydrochloric acid, however, (propenyl) dichloro- 
hydrin * is produced, 

C 3 H 5 (OH) 3 + 2HC1 = C 3 H 5 C1 2 -OH + 2H 2 0. 

Glyceryl trichloride (propenyl trichloride), CH 2 C1-CHC1- 
CH 2 C1, cannot easily be obtained by heating glycerol with 
hydrochloric acid, but may be prepared by treating the 
dichlorohy drin with phosphorus pentachloride, 

C 3 H 5 C1 2 .OH + PC1 5 = C 3 H 5 C1 3 + POC1 3 + HC1 ; 

it is a colourless liquid, boiling at 158, and smells like 
chloroform. The name ' glycerylj or propenyl, is sometimes 

given to the group of atoms -CH 2 -CH-CH 2 -, which may be 
regarded as a trivalent radicle. 

Chlorohydrin and dichlorohy drin both exist in two isomeric forms, 
CH 2 (OH).CH(OH).CH 2 C1 CH 2 (OH).CHC1-CH 2 -OH 

a-Chlorohydrin. /3-Chlorohydrin, 

CH 2 C1-CH(OH) CH 2 C1 CH 2 C1 CHC1 CH 2 -OH. 

-Dichlorohydrin. a/3-Dichlorohydrin. 

* The simple names ' chlorohydrin ' and ' dichlorohydrin ' originally 
given to these glycerol derivatives (and still used) are not satisfactory, 
and do not express their relation to glycerol. 
or*. Q 



258 TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 

o.'Chlorohydrin is formed, together with small quantities of the 
/3-compound, when glycerol is heated at 100 with hydrochloric 
acid ; it is an oily liquid, soluble in water. fi-Chlorohydrin can 
be obtained by treating allyl alcohol (p. 260) with hypochlorous 
acid. 

aa-Dichlorohydrin is produced when glycerol is heated with 
a solution of hydrogen chloride in glacial acetic acid ; it is a 
mobile liquid, only sparingly soluble in water, and on oxida- 
tion with chromic acid it yields symmetrical dichloracetone, 
CH 2 C1.CO CH 2 C1. 

ap-Dichlorohydrin is obtained on treating allyl alcohol (p. 
260) with chlorine ; on oxidation with nitric acid it gives 
a/3-dichloropropionic acid, CH 2 C1-CHC1-COOH. When treated 
with potash, both aa- and a/3-chlorobydrin yield epichlorohydrin, 
CH 2 C1-CH-CH 2 (compare ethylene oxide, p. 228). 



Y 



When glycerol is treated with acetyl chloride it does not yield 
triacetin, as might have been expected, but diacetylchlorohydrin, 

C 3 H 5 (OH) 3 + 2CH 3 .COC1 = C 3 H 5 C1(0-CO CH 3 ) 2 + H 2 O + HC1. 
This behaviour, although apparently abnormal, is not really so ; in 
the first place, the glycerol is converted into a G?mcefa/?-derivative 
in the usual manner, 

C 3 H 5 (OH) 3 + 2CH 3 -COC1 = C 3 H 5 (0-CO-CH 3 ) 2 -OH + 2HC1, 
and the hydrogen chloride produced during the reaction then acts 
on the diacetyl-derivative, just as it does on other monohydric 
alcohols, 

C 3 H 5 (0-CO-CH 3 ) 2 .OH + HC1 = C 3 H 5 (0 CO CH 3 ) 2 C1 + H 2 0. 
Ethylene glycol and other di- and poly-hydric alcohols show a 
similar behaviour. 

Nitro-glycerin, glyceryl trinitrate, or propenyl trinitrate, 
C 3 H 5 (0-N0 2 ) 3 , is the glyceryl ester of nitric acid. It is 
prepared by slowly adding pure glycerol drop by drop, or 
in a fine stream, to a well-cooled mixture of concentrated 
sulphuric acid (4 parts) and nitric acid of sp. gr. 1-52 (1 part) ; 
the solution is run into cold water, and the nitro-giycerin, 
which is precipitated as a heavy oil, washed well with water 
and left to dry in the air.* 

* Nitro-glycerin is an extremely dangerous substance, and its preparation 
is only safe to expert chemists. 



TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 259 

It is a colourless oil of sp. gr. 1-6, has a sweetish taste, and 
is poisonous; although readily soluble in ether, it is only 
sparingly soluble in alcohol, and insoluble in water, so that, as 
regards solubility, its behaviour is almost the exact opposite of 
that of glycerol, a fact which shows the influence of hydroxyl- 
groups in a very distinct manner. It explodes with great 
violence when suddenly heated, or when subjected to per- 
cussion, but when ignited with a flame it burns without 
explosion, and is even rather difficult to ignite. 

Nitro-glycerin is readily hydrolysed by boiling alkalies, 
being converted into glycerol and a nitrate,* 

C 8 H 6 (0-N0 2 ) 8 + 3KOH = C 3 H 5 (OH) 3 + 3KN0 3 ; 
on reduction with ammonium sulphide (p. 56) it yields glycerol 
and ammonia, 
C 3 H 5 (0-1S"0 2 ) 3 + 12H 2 S = C 3 H 5 (OH) 3 + 3NH 3 + 6H 2 + 12S. 

In these two reactions the behaviour of nitro -glycerin is exactly 
analogous to that of ethyl nitrate, CH 3 -CH 2 -0-NO 2 , but quite 
different from that of nitro-ethane, CH 3 -CH 2 -N0 2 , which, as pre- 
viously stated, is not decomposed by alkalies, and on reduction yields 
amido-ethane or ethylamine ; since, moreover, groups of atoms in 
a similar state of combination show a similar behaviour, it is clear 
that nitro-glycerol, like ethyl nitrate, is an ester, and not a nitro- 
derivative ; in other words, the nitro-groups (-NO 2 ) in nitro- 
glycerin are directly combined with oxygen, and not with carbon. 
The name nitro-glycerin is therefore misleading, but, being so 
well known, it is employed here instead of the more correct names, 
glyceryl trinitrate or propenyl trinitrate. 

Nitro-glycerin is extensively employed as an explosive, 
sometimes alone, sometimes in the form of dynamite, which 
is simply a mixture of nitro-glycerin and kieselguhr, a porous, 
earthy powder, consisting of the siliceous remains of small 
marine animals; the object of absorbing the nitro-glycerin 
with kieselguhr is to render it less liable to explode, and, 
consequently, safer to handle and to transport. The presence 

* An alkali nitrite is also formed owing to reduction, the glycerol 
undergoing partial oxidation. 



260 TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 

of acids in nitro-glycerin makes it liable to undergo spon- 
taneous decomposition and explosion ; great care must there- 
fore be taken in washing it thoroughly. Nitro-glycerin is 
also employed, mixed with gun-cotton (p. 282), as blasting- 
gelatine, and in the preparation of smokeless gunpowder 
(cordite) ; it is used in medicine in cases of heart disease. 

Unsaturated Compounds related to Glycerol. 

Allyl alcohol, CH 2 :CH-CH 2 .OH, is formed when anhydrous 
glycerol is slowly heated with crystallised oxalic acid until 
the temperature rises to about 260, and :the distillate then 
fractionated ; in the first place, the glycerol is converted into 
monoformin, with evolution of carbon dioxide, water, and a 
little formic acid (p. 147), 

C 3 H 5 (OH) 3 + C 2 H 2 4 = C 3 H 5 (OH) 2 .0-CHO + C0 2 + H 2 
C 3 H 5 (OH) 2 .OCHO + H 2 - C 3 H 5 (OH) 3 + H-COOH, 

but, on further heating, the rest of the monoformin undergoes 
decomposition, and allyl alcohol collects in the receiver, 

CH 2 (OH).CH(OH).CH 2 .O.CHO = 

CH 2 (OH)-CH:CH 2 + C0 2 + H 2 0. 

Allyl alcohol is also produced when acrolein (acraldehyde, 
p. 262) is treated with nascent hydrogen, a change which is 
exactly analogous to the formation of alcohol from aldehyde, 

CH 2 :CH-CHO + 2H - CH 2 :CH.CH 2 -OH. 

It is a colourless, neutral liquid, boils at 96-97, and has a 
very irritating smell ; it is miscible with water, alcohol, and 
ether in all proportions. 

Allyl alcohol is an unsaturated compound, and has there- 
fore not only the properties of a primary alcohol, but also 
those of unsaturated compounds in general. Its alcoholic 
character is shown by the following facts : it dissolves sodium 
with evolution of hydrogen, 

2CH 2 :CH.CH 2 -OH + 2Na = 2CH 2 :CH-CH 2 .ONa + H 2 ; 



TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 261 

forms ethereal salts with acids, 

CH 2 :CILCH 2 .OH + HC1 = CH 2 :CH.CH 2 C1 + H 2 ; 

and on oxidation is converted, first into acrolein, then into 
acrylic acid, 

CH.,:CILCH 2 .OH + - CH 2 :CH-CHO + H 2 
CH 2 :CH-CH 2 .bH + 20 = CH 2 :CILCOOH + H 2 0. 

In all these reactions its behaviour is so closely analogous to 
that of ethyl alcohol and other primary alcohols, that it must 
be concluded that allyl alcohol contains the group -CH 2 -OH. 
That it is an unsaturated compound is shown by its be- 
haviour with chlorine and bromine, with which it combines 
directly, forming a/2-dichloro- or a/3-dibromohydrin, isomeric 
with the corresponding aa- compounds obtained by treating 
glycerol with halogen acids, 

CH 2 :CH-CH 2 .OH + Br 2 - CH 2 Br.CHBr.CH 2 -OH. 

Allyl iodide, CH 2 :CH-CH 2 I, is an unsaturated ester, 
related to allyl alcohol in the same way as ethyl iodide to 
ethyl alcohol. It may be obtained by treating allyl alcohol 
with iodine and phosphorus, but is more conveniently pre- 
pared directly from glycerol. 

For this purpose iodine (10 parts) is dissolved in glycerol (15 
parts), and small pieces of dry phosphorus (6 parts) added from 
time to time, the mixture being very gently warmed if necessary to 
start the reaction ; the operation is conducted in a large retort 
connected with a condenser, a stream of carbon dioxide being 
passed through the apparatus during the experiment. It is 
probable that the glycerol is first converted into the tri-iodide, 
CH 2 LCHLCH 2 I, which then undergoes decomposition into iodine 
and allyl iodide ; if excess of phosphorus and iodine be employed 
isopropyl iodide is formed, 

CH 2 :CH CH 2 I + HI = CH 2 :CH-CH 3 + 1 2 
CH 2 :CH-CH 3 + HI = CH 3 CHI CH 3 . 

Allyl iodide is a colourless liquid, boiling at 101, and has 
an odour of garlic ; it resembles ethyl iodide in many respects, 
but has also the properties of an unsaturated compound, 



262 TRIHYDR1C AND POLYHYDRIC ALCOHOLS. 

When heated with potassium sulphide in alcoholic solution 
it is converted into allyl sulphide (see below), just as ethyl 
iodide gives ethyl sulphide, 

2CH 2 :CH-CH 2 I + K 2 S = (CH 2 :CILCH 2 ) 2 S + 2KL 

Allyl bromide, CH 2 :CH-CH 2 Br, may be obtained by treat- 
ing allyl alcohol with phosphorus tribromide ; it is a heavy 
liquid, and boils at 70-71. 

Allyl sulphide occurs in nature in many Cruciferse, but is 
especially abundant in garlic (Alii am sativum}, from which 
it is obtained by distilling the macerated plant with water ; 
it is therefore known as oil of garlic. It is a colourless, very 
unpleasant-smelling liquid, boiling at 140. Another allyl 
derivative namely, allyl isothiocyanate, occurs in nature in 
considerable quantities in black mustard-seeds, and is known 
as oil of mustard (p. 298). 

Acrolem, or acraldehyde, CH 2 :CH-CHO, is formed during 
the partial combustion of fats, and when impure glycerol 
is distilled under ordinary pressure ; also when allyl alcohol 
undergoes oxidation. It is prepared by distilling glycerol 
with some dehydrating agent, potassium hydrogen sulphate 
being usually employed, 

C 3 H 5 (OH) 3 = C 3 H 4 + 2H 2 0. 

Acrolein is an aldehyde, and is related to allyl alcohol in 
the same way as aldehyde to ethyl alcohol; it is a colour- 
less liquid, boils at 52, and has an exceedingly irritating and 
disagreeable odour, like that of scorched fat; it produces 
sores when brought in contact with the skin, and its vapours 
cause a copious flow of tears. Like other aldehydes, it 
reduces ammoniacal solutions of silver hydroxide with forma- 
tion of a mirror, and readily undergoes polymerisation into 
an amorphous, brittle substance named disacryl ; it also gives 
the aldehyde reaction with rosaniline, but, on the other hand, 
it does not combine with sodium hydrogen sulphite. On 
reduction it yields allyl alcohol ; on exposure to the air, or 
on treatment with silver oxide, it readily undergoes oxidation, 



TR1HYDRIC AND POLYHYDRIC ALCOHOLS. 263 

yielding acrylic acid. That it is an unsaturated compound is 
shown by the fact that it combines directly with bromine, 
forming an additive-product of the composition, 

CH 2 Br.CHBr.CHO. 

Crotonaldehyde, CH 3 CH:CH CHO, is a homologue of acralde- 
hyde ; it is obtained on heating acetaldehyde with dilute hydro- 
chloric acid, or with a solution of zinc chloride, aldol being formed 
as an intermediate product (p. 126), 

2CH 3 -CHO = CH 3 -CH(OH).CH.,-CHO 
CH 3 .CH(OH)-CH 2 -CHO = CH 3 -CH :CH CHO + H 2 O. 

It boils at 104-105, and closely resembles acraldeliyde in properties ; 
on reduction it yields, first, crotonalcohol, CH 3 -CH:CH-CH 2 -OH, 
and then butyl alcohol, CH 3 -CH Q -CH 2 -CH 2 -OH ; on oxidation it 
gives crotonic acid, CH 3 -CH:CH COOH. 

Acrylic acid, CH 2 :CH-COOH, the oxidation product of 
allyl alcohol and of acrolein, may also be obtained from 
hydracrylic acid (p. 233), which on distillation loses the 
elements of water, 

CH 2 (OH).CH 2 .COOH = CH 2 :CH-COOH + H 2 0, 

a change analogous to the formation of ethylene from alcohol ; 
acrylic acid is also produced when /3-bromopropiouic acid is 
treated with alcoholic potash, just as ethylene is formed from 
ethyl bromide, 

CH 2 Br.CH 2 .COOH = CH 2 :CILCOOH + HBr. 

Acrylic acid is a liquid at ordinary temperatures, and boils at 
139-140; it smells like acetic acid, is miscible with water in 
all proportions, and its solutions have an acid reaction. It is 
a monocarboxylic acid, and forms metallic and ethereal salts 
just as do the fatty acids ; it differs from the latter, however, 
in being an unsaturated compound, as is shown by its forming 
additive-products. It combines directly with bromine, giving 
dibromopropionic acid, 

CH 2 :CH.COOH + Br 2 = CH 2 Br.CHBr.COOH ; 



264 TRinrDRic AND POLYHYDRIC ALCOHOLS. 

with halogen acids, yielding ^-halogen derivatives* of pro- 
pionic acid, 

CH 2 :CH-COOH + HC1 = CH 2 C1-CH 2 .COOH, 
and with nascent hydrogen, giving propionic acid, 
CH 2 :CILCOOH + 2H = CH 3 .CH 2 -COOH. 

Crotonic acid, CH 3 .CH:CH-COOH, the next homologue of acrylic 
acid, may be obtained by methods similar to those mentioned in the 
case of acrylic acid namely, by the oxidation of crotonalcohol or 
of crotonaltlehyde, by the distillation of /Miydroxybutyric acid, 
CH 3 .CH(OH).CH 2 -COOH, and by treating a-bromobutyric acid with 
alcoholic potash. It melts at 72, and resembles acrylic acid in 
general behaviour. 

Ole'ic acid, C 18 H 34 2 , one of the higher members of the acrylic 
series, has been previously mentioned (p. 171). 

PolyJiydric Alcohols. 

The existence of tetra-, penta-, and hexa-hydric alcohols, 
which theoretically should be obtained from the higher 
paraffins by the substitution of four, five, or six hydroxyl- 
groups for an equivalent quantity of hydrogen, just as glycerol 
is derived from propane, was of course to be expected ; never- 
theless, owing to the difficulties which would be met with in 
the actual synthesis of such complex compounds from the 
paraffins, or from other compounds, it is highly probable that 
they might still have been unknown, were it not that many 
of them occur in nature, and may also be prepared from 
products of the vegetable kingdom by simple processes. 

Erythritol, CH 2 (OH).CH(OH).CH(OH).CH 2 -OH, for ex- 
ample, is a tetrahydric alcohol which occurs in many lichens, 
and in certain seaweeds. AraUtol and xylitol are penta- 
hydric alcohols of the constitution, 

CH 2 (OH)-CH(OH).CH(OH).CH(OH).CH 2 .OH; 
they may be respectively prepared by reducing arabinose and 
xylose, two sugar-like compounds, which occur in various 
vegetable products, with sodium amalgam and water. 

* This behaviour is abnormal, as the halogen usually combines with that 
carbon atom which is combined with the least number of hydrogen atoms (p. 80). 



TRIHYDRIC AND POLYHYDRIC ALCOHOLS. 265 

HeXahydric alcohols, such as mannitol, sorbitol, and clul- 
citol, also occur in nature ; these three compounds are identical 
in ordinary chemical constitution, and they may all be repre- 
sented by the formula, 

CH 2 (OH).CH(OH)-CH(OH).CH(OH).CH(OH).CH 2 .OH; 

their relationship is analogous to that of the tartaric acids 
(p. 250), and they are optically isomeric (Part II. p. 555). 

Mannitol is found in manna, the dried sap of a species of 
ash, from which it may be extracted with boiling alcohol ; 
it may also be obtained by reducing mannose or fructose 
(pp. 269, 270) with sodium amalgam and water. It is a 
colourless, crystalline substance, has a sweet taste, and is 
readily soluble in water and hot alcohol, but insoluble in 
ether. When carefully oxidised with nitric acid it yields the 
aldehyde, mannose, and the ketone, fructose ; on reduction 
with hydriodic acid it is converted into (secondary*) hexyl 
iodide, a derivative of normal hexane, 

CH 2 (OH).CH(OH).CH(OH).CH(OH)-CH(OH).CH 2 .OH 
+ 11 HI = CH 3 .CH 2 .CH 2 .CH 2 .CHLCH 3 + 6H 2 + 5I 2 . 

This conversion of mannitol (sorbitol and dulcitol) into a derivative 
of normal hexane is a fact of great importance, as it throws much 
light on the constitution not only of mannitol, but also on that of 
the monoses (p. 267) in general ; since the latter yield one or other 
of these hexahydric alcohols on reduction with sodium amalgam 
and water, it is proved that they also are derivatives of normal 
hexane, and not of some secondary or tertiary paraffin, isomeric 
with hexane. 

The constitution of mannitol is further established by the usual 
methods ; that it contains six hydroxyl-groups is shown by the fact 
that it yields a hexacetyl -derivative, C 6 H 8 (OCO-CH 3 ) 6 , and a hexa- 
nitrate, C 6 H 8 (O-N0 2 ) 6 . As, moreover, it is known from experience 
that in all stable hydroxy-compounds one carbon atom does not 
unite with more than one hydroxyl-group, each of the six hydroxyl- 
groups in mannitol must be combined with a different carbon atom. 

* The term ' secondary ' which is always applied to this compound is 
rather misleading, and seems to be based on the fact that the iodide may be 
regarded as a derivative of secondary hexyl alcohol, 

CH 3 .CH 2 -CH 2 .CH 2 .CH(OH)-CH 3 . 



266 THE CARBOHYDRATES. 

CHAPTER XV. 

THE CARBOHYDRATES. 

The compounds usually known as the carbohydrates do not 
form a well-defined group, inasmuch as the term is applied 
to substances widely different both in properties and in 
constitution ; they may, however, be roughly described as 
naturally occurring substances, composed of carbon, hydrogen, 
and oxygen, in which the ratio of hydrogen to oxygen is the 
same as in water. The word ' carbohydrate ' was originally 
given to such compounds because they might be represented 
as composed of carbon and water in different proportions : 
glucose, C 6 H 12 6 , for example, might be represented as 
6C + 6H 2 0, a mode of expression which, if employed now, 
would be both useless and misleading. 

The carbohydrate group is one of the most important in 
organic chemistry, as it includes many of the principal con- 
stituents of plants. To this group belong (a) the sugars, 
substances which are of great value as food-stuffs and as 
sources of alcohol, and to which the sweetness of fruits is 
due ; (b) the starches, the most abundant of all foods ; and 
(c) the celluloses, substances of which the cell membranes and 
tissues of plants are principally composed, and which in the 
form of cotton, paper, wood, &c., are of the greatest import- 
ance in daily life. 

The Sugars. 

The sugars described in the following pages may be classed 
into two groups : (a) the monoses having the molecular for- 
mula C 6 H 12 6 , and (b) the Hoses having the molecular formula 
C 12 H 22 O n ; the former are not decomposed by very dilute 
acids, but the latter readily undergo hydrolysis yielding two 
molecules of the same or of different monoses. 



THE CARBOHYDRATES. 267 

MONOSES. 

Glucose, C 6 H 12 6 , or CH 2 (OH).[CH-OH]}.CHO, also called 
dextrose, or grape-sugar, is found in large quantities in 
grapes hence its name, grape-sugar ; when the grapes are 
dried in the sun, in the preparation of raisins, the glucose 
in the juice is deposited in hard, brownish-coloured nodules. 
Glucose is more frequently met with associated with fructose, 
mixtures of these sugars occurring in the juices of a great 
many sweet fruits, and also in the roots and leaves of plants, 
and in honey. Pure glucose may be prepared from sucrose 
(cane-sugar) by inversion with acids (p. 276) and recrystal- 
lisation of the product (invert sugar) from alcohol, when the 
more readily soluble fructose remains in solution. 

Alcohol (1 litre, 90 per cent. ) is mixed with concentrated hydro- 
chloric acid (40 c.c.), heated at about 50, and powdered sucrose 
(350 grams) added in small portions, the whole being well stirred 
during the operation. The mixture is now kept for two hours at 
this temperature, then allowed to cool, and crystallisation promoted 
by stirring, or, better, by the addition of a crystal of glucose. After 
some days the crystals are collected and purified by recrystallisa- 
tion from 80 per cent, alcohol. 

Glucose crystallises with 1 mol., H 2 0, in warty masses 
which melt at 86, the anhydrous substance melting at 
146; it is almost insoluble in absolute alcohol, but soluble 
in about its own weight of water at ordinary temperatures, 
the solution being less sweet than that of sucrose. It is 
not carbonised when gently warmed with sulphuric acid 
(distinction from sucrose); its solutions are dextrorotatory t 
that is, they have the property of rotating the plane of 
polarisation of polarised light to the right hence the name 
dextrose by which it was formerly known. The strength 
of a solution of sucrose may be estimated by determining 
the amount of rotation which is produced by a column 
of the liquid of known length. The apparatus used for 

* Compare foot-note, p. 1 37. 

+ Mr>= +52-7 in 10 per cent, aqueous solution. 



268 THE CARBOHYDRATES. 

this purpose is called a saccharimeter or polarimeter, and 
the operation itself, saccharimetry. 

Glucose is a strong reducing agent, and quickly pre- 
cipitates gold, silver, and platinum from solutions of their 
salts on warming. If a solution of glucose be mixed with 
potash, and then copper sulphate added, -a deep-blue solution 
is obtained, and on gently warming, a bright-red precipitate 
of cuprous oxide , Cu 2 0, is deposited, the solution becoming 
colourless if sufficient glucose be added ; as, moreover, a 
given quantity (1 molecule) of glucose always reduces exactly 
the same quantity (approximately 5 molecules) of cupric to 
cuprous oxide, this behaviour affords a method of estimating 
glucose by simple titration. 

The solution used for this purpose is known as Fehling's solution, 
and as it decomposes on keeping, it is best prepared, as required, by 
mixing equal quantities of the following solutions : (1) 34-6 grams 
of crystallised copper sulphate, made up to 500 c.c. with water; 
(2) 173 grams of Rochelle salt and 60 grams of sodium hydrate, 
made up to 500 c.c. with water. 10 c.c. of the deep-blue solution 
thus obtained are completely reduced that is, the colour dis- 
charged by 0-05 gram of dextrose, or by 0-0475 gram of sucrose 
(after inversion). 

Glucose ferments readily with yeast in dilute aqueous 
solution at a temperature of about 20-30, yielding princi- 
pally alcohol and carbon dioxide, 



but at the same time fusel-oil and small quantities of 
glycerol, succinic acid, and other substances are formed. 

Like sucrose, glucose combines readily with certain metal- 
lic hydroxides, forming glucosates, such as calcium glucosate, 
C 6 H n (CaOH)0 6 , and barium glucosate, C 6 H n (BaOH)0 6 ; 
these compounds are readily soluble in water, and are de- 
composed by carbonic acid, with regeneration of glucose. 

Glucose givesa pentacetyl derivative, C 5 H 6 (0-CO-CH 3 ) 5 -CHO, 
when warmed with acetic anhydride and a little zinc chloride, 
showing that it contains five hydroxyl-groups, and is there- 



THE CARBOHYDRATES. 269 

fore a pentdhydric alcohol ; it has also the properties of an 
aldehyde, and its constitution may be expressed by the 
formula, 

CH 2 (OH).CH(OH)-CH(OH).CH(OH).CH(OH).CHO, 
which is based on a number of facts, only a few of which 
can be given here. 

On reduction with sodium amalgam in aqueous solution, it 
is converted into the primary alcohol, sorbitol, 

CH 2 (OH).[CH-OH] 4 .CHO + 2H = 

CH 2 (OH).[CH.OH] 4 .CH 2 .OH ; 

whereas when oxidised with bromine water it yields gluconic 
acid, CH 2 (OH)-[CH-OH] 4 .COOH. These changes are clearly 
analogous to those undergone by acetaldehyde, and the fact 
that gluconic acid contains the same number of carbon 
atoms as glucose, shows that the latter is an aldehyde 
and not a ketone (p. 142). Powerful oxidising agents, 
such as nitric acid, convert glucose into saccharic acid, 
COOH-[CH.OH] 4 .COOH, the -CH 2 -OH group, as well as 
the -CHO group, undergoing oxidation ; ultimately it is re- 
solved into oxalic acid. Glucose, like other aldehydes, inter- 
acts readily with hydroxylamine and with phenylhydrazine, 
with formation of the oxime, CH 2 (OH).[CH-OH] 4 -CH:NOH, 
and the hydrazone (p. 272), 

CH 2 (OH).[CH.OH] 4 .CH:N 2 H.C 6 H 5 . 

Mannose, C 6 H 12 6 , or CH 2 (OH).[CH(OH)] 4 -CHO, is a sugar 
closely related to glucose, with which it is identical in chemical 
constitution, but from which it differs in its action on polarised 
light ; it is obtained by oxidising mannitol with nitric acid, 
and by hydrolysing seminin (contained in various vegetable 
products such as ivory-nuts) with dilute sulphuric acid. 

Galactose, C 6 H 12 6 , or CH 2 (OH).[CH.OH] 4 -CHO, is formed by 
the hydrolysis of lactose, together with glucose, from which it may 
be separated by crystallisation from water. It is also formed by 
boiling gum-arabic and other gums with dilute sulphuric acid. 



270 THE CARBOHYDRATES. 

It crystallises in prisms, melts at 168, and its solutions are 
dextrorotatory, and ferment readily Avith yeast. When oxidised 
with nitric acid it yields mucic acid, COOH-[CH-OH] 4 -COOH, 
which is optically isomeric with saccharic acid. It interacts with 
phenylhydrazine, yielding galactosazone, 

CH 2 (OH)-[CH.OH] 3 .C(N 2 HC 6 H 5 ) CH:N 2 HC 6 H 5 ; 
and on reduction with sodium amalgam and water it is converted 
into the corresponding alcohol, dulcitol, CH 2 (OH)-[CH-OH] 4 -CH 2 -OH, 
which is isomeric with mannitol (p. 264). 

Fructose, C 6 H 12 6 , or CH 2 (OH).[CH.OH] 3 .CO-CH 2 .OH 5 
also called levulose, occurs, together with glucose, in most 
sweet fruits and in honey ; it may be prepared from invert 
sugar (p. 276) by taking advantage of the fact that its lime 
compound is sparingly soluble in water, whereas that of 
glucose is readily soluble. 

Invert sugar (10 grams) is dissolved in water (50 c.c.), the 
solution well cooled with ice, and slaked lime (6 grams) added 
in small quantities at a time, with constant stirring. The 
sparingly soluble lime compound of fructose is collected on a 
filter, washed with a little water, well pressed, and then decom- 
posed by suspending it in water, and passing carbon dioxide; 
the filtrate yields, on evaporation, nearly pure fructose as a 
transparent syrup. 

Pure crystallised fructose is prepared from mulin, 
(C 6 H 10 5 )ft, a starch which occurs in many plants, and 
especially in dahlia tubers ; for this purpose the inulin is 
simply boiled with dilute sulphuric acid, 

(C 6 H 10 0> + rcH 2 = raC 6 H 12 6 . 

An aqueous solution of inulin is heated on a water-bath for one 
hour, with a few drops of sulphuric acid ; the sulphuric acid is then 
removed by precipitation with barium hydroxide, and the solution 
evaporated at 80. On the addition of a crystal of fructose the 
syrup slowly solidifies, and the crystals may then be purified by 
recrystallisation from alcohol. 

Fructose separates from alcohol in small, bard crystals, and 
melts at 95 ; it is more soluble in water and alcohol than 
glucose, and its taste is just about as sweet as that of the 



THE CARBOHYDRATES. 271 

latter. Fructose is levorotatory* hence the name Mevulose' 
by which it was formerly known. 

Fructose ferments with yeast, but less rapidly than 
glucose ; consequently, in fermenting a solution of invert 
sugar, the glucose is decomposed first, and the operation 
can be stopped at a point when the solution contains only 
fructose ; by the further action of yeast, however, the fructose 
also undergoes fermentation, yielding the same products as 
glucose (p. 268). 

Fructose is a strong reducing agent, and reduces Fehling's 
solution more rapidly than, although to exactly the same 
extent as, glucose ; this behaviour is due to the presence of 
the group -COCH 2 -OH, and all those ketonic alcohols which 
contain this group are strong reducing agents. 

Fructose has the properties of a pentaliydric alcohol, as well 
as those of a ketone, and its constitution may be expressed by 
the formula, 

CH 2 (OH).CH(OH).CH(OH).CH(OH)-CO.CH 2 .OH. 

When digested with acetic anhydride and zinc chloride, 
it yields a pentacetyl derivative, C 6 H 7 0(C'CO-CH 3 ) 5 , a fact 
which shows that it contains five hydroxyl-groups. It is 
reduced by sodium amalgam and water more readily than 
'glucose, mannitol (and sorbitol) being formed, 

CH 9 (OH){CH.OH] 3 -CO.CH 2 .OH + 2H = 

CH 2 (OH){CH.OH] 3 -CH(OH).CH 2 .OH, 

just as acetone, under similar treatment, yields isopropyl 
alcohol. When oxidised with nitric acid or bromine water, 
it yields tartaric acid and glycollic acid, 

CH 2 (OH).CH(OH).CH(OH).CH(OH).|CO.CH 2 .OH + 40 = 
COOH.CH(OH).CH(OH).COOH + CO'OH-CH 2 .OH + H 2 ; 

whereas, when boiled with mercuric oxide in aqueous solution, 
it is oxidised to trihydroxybutyric acid and glycollic acid, 

* ["]D -93 in 10 per cent, aqueous solution. 



272 THE CARBOHYDRATES. 

CH 2 (OH).CH(OH).CH(OH).CH(OH).;CO-CH 2 .OH + 20 = 

CH 2 (OH).CH(OH).CH(OH).COOH + COOILCH 2 .OH. 

Tins behaviour shows that fructose is a ketone, and not an 
aldehyde ; it does not, like glucose, yield, on oxidation, an 
acid containing the same number of carbon atoms, but is 
decomposed in a variety of ways, giving products which throw 
light on its constitution. 

Fructose, like other ketones, interacts with hydroxylamine, 
yielding the oxime, CH 2 (OH).[CH.OH] 3 .C(NOH).CH 2 .OH, 
and with phenylhydrazine (see below) ; it also combines 
directly with hydrocyanic acid. 

Glucose and fructose have recently been prepared syn- 
thetically from formaldehyde and also from glycerol. When 
an aqueous" solution of formaldehyde is treated with milk of 
lime at ordinary temperatures, a sugar-like substance called 
metJiylenitan (Butlerow) ovformose (Loe w) is produced. Methy- 
lenitan and formose consist of mixtures of various sugars of 
the composition C 6 H 12 6 , produced by the polymerisation of 
formaldehyde, 

6CH 2 - C 6 H 12 6 . 

From these mixtures E. Fischer isolated a sugar which he 
called a-acrose, and from which, by a series of operations too 
numerous to discuss here, he succeeded in preparing both 
glucose and fructose. 

a-Acrose was also obtained by E. Fischer and Tafel from glycerose, 
which is a mixture of glyceraldehyde, CH 2 (OH)-CH(OH)-CHO, and 
dihydroxyacetone, CH 2 (OH)-CO-CH 2 -OH, prepared by carefully 
oxidising glycerol with bromine water or dilute nitric acid ; 
when glycerose is treated with caustic soda it undergoes con- 
densation, giving a mixture of sugars, among others, a-acrose. 

Action of Phenylhydrazine on Glucose and Fructose. 

When glucose and fructose are treated with phenylhydrazine 
(1 mol.) they yield hydrazones, just as do other aldehydes and 
ketones, 



THE CARBOHYDRATES. 



273 



*M-CH(OH) CHO + C 6 H 5 -NH-NH 2 = 

Glucose. M-CH(OH).CH:N 2 HC 6 H 5 + H 2 O. 

Glucosephenylhydrazone. 

6 H 5 .NH-NH 2 = M C(N 2 HC 6 H 5 ).CH 2 .OH + H 2 0. 



M-CO CH 2 

Fructose. 



Fructosephenylhydrazone. 



These hydrazones, when heated with excess of phenylhydrazine, 
undergo oxidation, the ]>CH-OH group of the one and the 

CH 2 -OH group of the other being transformed into CO and 

CHO, respectively, by loss of hydrogen, which reduces some of 
the phenylhydrazine to aniline (Part II. p. 373) and ammonia, 

C 6 H 5 -NH-NH 2 + 2H = C 6 H 5 -NH 2 + NH 3 . 

The ketone or aldehyde thus formed then combines with a second 
molecule of phenylhydrazine, with formation of an osazone, 



Hydrazones. 

M 
CHOH 



c^ 



H:N 2 HC 6 H, 



C:N 2 HC 6 H 5 
CHo-OH 




sazon, 



C:N 2 HC 6 H 6 
CHO 



:N 2 HC 6 H 5 
CH:N 2 HC 6 H 5 



Although the hydrazones of glucose and fructose are quite distinct 
substances, they yield one and the same osazone ; this fact proves 
that the two sugars differ in constitution only as regards the two 
terminal groups. 

Many other sugars yield hydrazones or osazones according as 
1 inol., or excess, of phenylhydrazine is employed. The hydrazones 
are usually readily soluble in water, but the osazones are only 
sparingly soluble ; the latter are therefore of the greatest service, 
not only in the detection and identification of a sugar, but also as 
offering a means of isolating it from a mixture. 

When treated with strong hydrochloric acid, the osazones are 
decomposed with separation of phenylhydrazine hydrochloride, 
and formation of osones, substances which contain the group 
CO-CHO, and which are therefore both ketones and aldehydes, 

* The group CH 2 (OH).CH(OH).CH(OH)-CH(OH)-, which takes no part 
in the reaction, is represented by M, for the sake of clearness, 

Org R 



274 THE CARBOHYDRATES. 

M-C(N 2 HC 6 H 5 )-CH :N 2 HC 6 H 5 + 2HC1 + 2H 2 O = 

Glucosazone. 
M.COCHO + 2C 6 H 5 .NH-NH 2 , HC1. 

Glucosone. 

As, moreover, osones may be reduced to sugars with the aid of 
zinc dust and acetic acid, the osazones may be indirectly reconverted 
into a sugar. A given osazone, however, does not necessarily 
yield the sugar from which it was derived ; glucosazone, for 
example, yields first glucosone and then fructose (the group 
CO-CHO in the osone being converted into CO-CH 2 -OH), 
M-CO-CHO + 2H = M-CO CH 2 -OH. 

Glucosone. Fructose. 

This series of reactions affords, therefore, a means of converting 
glucose into fructose (E. Fischer). 

BIOSES. 

Sucrose, or cane-sugar (saccharose), C 12 H 22 O n , is very widely 
distributed in nature ; it occurs in large quantities in the ripe 
sugar-cane (15-20 per cent.) and in beetroot (some kinds of 
which contain as much as 16 per cent.), in smaller quantities in 
strawberries, pine-apples, and other fruits. 

The sugar-cane and beetroot are the raw materials from 
which practically the whole of the sucrose of commerce is 
manufactured, the processes of extraction being much the 
same in both cases, and requiring expensive apparatus in 
order to obtain the largest possible yield of crystallised 
sucrose. 

The material is crushed in hydraulic presses, and the expressed 
juice boiled with about 1 per cent, of milk of lime, in order to 
neutralise acids present, and to coagulate the vegetable albu- 
minoids which are always contained in the extract, and thus 
prevent fermentation. The solution is treated with carbon dioxide, 
in order to precipitate any excess of lime, decolourised as far as 
possible by boiling with animal charcoal, and filtered ; it is then 
evaporated under reduced pressure in an apparatus heated with 
steam, until the syrup is of such a consistency that it deposits 
crystals on cooling. These crystals are separated from the brown 
mother-liquor (molasses, or treacle) in a centrifugal machine, and 
purified by recrystallisation from water. 

The molasses still contain about 50 per cent, of sucrose, which 



THR CARBOHYDRATES. 275 

does not crystallise from the syrup even on further evaporation, 
owing to the presence of impurities ; nearly the whole of this 
sucrose, however, can be profitably extracted, by adding strontium 
hydroxide, and separating the insoluble strontium sucrate (see 
below) from the dark mother-liquor by filtration. This precipitate 
is suspended in water, decomposed by passing carbon dioxide, and 
the filtrate from the strontium carbonate evaporated to a syrup ; 
the impurities having now been removed, the sucrose separates in 
the crystalline form. The annual production of sucrose is about 
8-9 million tons. 

Sucrose crystallises from water in large four-sided prisms 
(sugar-candy), and is soluble in one-third of its weight of 
water at ordinary temperatures, but only sparingly soluble in 
alcohol. It melts at about 160-161, and on cooling does not 
immediately crystallise, but solidifies to a pale-yellow, glassy 
mass, called barley-sugar, which, however, on long standing, 
gradually becomes opaque and crystalline. At about 200-210 
sucrose loses water, and is gradually converted into a brown 
mass called caramel, which is largely used for colouring 
liqueurs, soups, gravies, &c. 

Warm concentrated sulphuric acid chars sucrose ; if a 
strong aqueous solution of sucrose be mixed with an equal 
volume of concentrated sulphuric acid, the mixture blackens 
and the carbonaceous product swells up enormously, owing to 
the evolution of steam, carbon dioxide, and sulphur dioxide. 

If a trace of a mineral acid be added to a solution of sucrose, 
and the liquid warmed or simply allowed to stand, the sucrose 
is hydrolysed, with formation of equal quantities of glucose 
and fructose, 

C 12 H 22 U + H 2 = C 6 H 12 6 + C 6 H 12 6 . 

Sucrose. Glucose. Fructose. 

Now, since fructose rotates the plane of polarisation to the 
left to a somewhat greater extent than glucose rotates it to 
the right, the product, which consists of equal parts of 
glucose and fructose, is slightly levorotatory. When, there- 
fore, a solution of sucrose, which is dextrorotatory* is boiled 

* []p= +66-5 in 10 per cent, aqueous solution. 



276 THE CARBOHYDRATES. 

with acids, the resulting solution is levorotatory that is 
to say, the direction of the rotation lias been reversed or 
' inverted.' Hence this process is usually called inversion, and 
the mixture of glucose and fructose is called invert sugar. 

Invert sugar comes into the market as a somewhat brownish 
mass, and is extensively used in the manufacture of preserves, 
confectionery, &c., as well as for the preparation of alcohol. 
Prolonged boiling with hydrochloric acid (sp. gr. 1-1) con- 
verts sucrose into levulinic acid (p. 200). 

Sucrose does not reduce Fehling's solution (p. 268), and it 
does not directly undergo alcoholic fermentation with yeast ; 
when, however, it is left for some time in contact with yeast, 
an enzyme, invertase, which is present in the yeast, con- 
verts it into glucose and fructose, and then alcoholic fermen- 
tation sets in. When boiled with acetic anhydride and 
sodium acetate, sucrose is converted into octacetylsucrose, 
C 12 H 14 O 3 (0-CO-CH 3 ) 8 , and therefore contains eight hydroxyl- 
groups ; this fact, and the behaviour of sucrose on hydrolysis, 
show that it is formed by the condensation of one molecule 
of glucose with one molecule of fructose, but its constitution 
has not yet been clearly established. 

Sucrose combines readily with certain hydroxides, such as those 
of calcium, barium, and strontium, with formation of metallic 
compounds called sucrosates (saccharosates), in which one or more 
of the hydroxyl-groups in the sucrose is displaced by the metal or 
hydroxide. These sucrosates are produced by simply mixing the 
sucrose solution with the metallic hydroxide. They are readily 
decomposed by much water and by carbon dioxide into sucrose and 
the hydroxide or carbonate of the metal. 

Strontium sucrosate, C 12 H 20 (SrOH) 2 O 11 , is a granular substance of 
great commercial importance, owing to its use in separating sucrose 
from molasses (p. 275). 

Maltose, C 12 H 22 O n , is produced together with dextrin 
(p. 280) by the action of malt on starch ; this change may be 
roughly represented by the equation, 

3(C 6 H 10 6 )n + nR 2 = C ia H M O u + wC 6 H 10 5 , 
and, as already stated in describing the manufacture of alcohol 



THE CARBOHYDRATES. 277 

and spirituous liquors, it is brought about by an unorganised 
ferment, diastase, which, is contained in the malt. 

Preparation of Maltose. Potato starch (1 kilo) is heated with 
water (4 litres) on a water-bath until it forms a paste, and after 
cooling to 60, malt (60 grams) is added, the mixture being kept at 
this temperature for an hour. The solution is then heated to boil- 
ing, filtered, and evaporated to a syrup, which crystallises on the 
addition of a crystal of maltose ; the crude substance is purified by 
washing with alcohol, and then recrystallising from this solvent. 

Maltose crystallises with one molecule of water in needles, 
and is very soluble in water, the solution being strongly 
dextrorotatory ; * it reduces Fehling's solution, but only about 
two-thirds as much as the same weight of glucose, and 
ferments readily with yeast. When boiled with dilute 
sulphuric acid, it is completely converted into glucose, 

C 12 H 22 O n + H 2 = 2C 6 H 12 6 , 

a change which indicates that maltose is an anhydride of the 
latter. 

Maltose interacts with phenylhydrazine, yielding maltosazone, 
C 12 H 20 9 (N 2 HC 6 H 5 ) 2 , and gives with acetic anhydride octacetyl- 
maltose, C 12 H 14 (C 2 H 3 O 2 ) 8 O 3 . 

Lactose, or milk sugar, C 12 H 22 O n , has so far only been 
found in the animal kingdom. It occurs in the milk of all 
mammals to the extent of about 4 per cent., and is obtained 
as a by-product in the manufacture of cheese. 

When milk is treated with rennet the casein separates, and 
lactose remains in solution ; on evaporation, the crude sugar 
is deposited in crystals, which are readily purified by re- 
crystallisation from water. 

Lactose forms large, hard, colourless crystals, which contain 
one molecule of water of crystallisation. It dissolves in six 
parts of water at ordinary temperatures, and is very much 
less sweet than sucrose ; it is dextrorotatory.! It reduces 
Fehling's solution on boiling, but much more slowly than 

* [] D = +139 in 10 per cent, aqueous solution. 

f [*] D = +52-53 in aqueous solution containing 10 per cent, of C 12 H 22 O 11 



278 THE CARBOHYDRATES, 

glucose. Like sucrose, it does not ferment with pure yeast, 
but ordinary yeast decomposes it into alcohol and lactic acid. 
When oxidised with nitric acid, it yields a mixture of sac- 
charic and mucic acids, both of which have the constitution 
COOH{CH-OH] 4 -COOH, and which differ from one another, 
like the tartaric acids, in their action on polarised light. 
Lactose is decomposed, by boiling with dilute sulphuric acid, 
into glucose and galactose (p. 269), 

C 12 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 . 

Lactose. Glucose. Galactose. 

POLYOSES. 

Starch, dextrin, and cellulose are all highly complex sub- 
stances, the molecules of which seem to consist of combina- 
tions of the molecules of the monoses or bioses, with loss of 
the elements of water; they are therefore classed together 



Starch, or amylum, (C 6 H 10 5 )?*, is widely disseminated 
throughout the vegetable world, and is found in almost all 
the organs of plants in the form of nodules. 

It occurs in large quantities in all kinds of grain, as, for 
example, in rice, barley, and wheat, and also in tubers, such 
as potatoes and arrowroot. In Europe starch is manufactured 
principally from potatoes, but sometimes also from wheat, 
make, and rice. 

The potatoes are well washed, crushed, and macerated with water 
in fine sieves, when the starch passes through with the water, 
leaving a pulp, consisting of gluten, cellulose, and other substances. 
The milky liquid, on standing, deposits the starch as a paste, which 
is repeatedly washed by decantation, and then slowly dried. 

The grain is first softened by soaking in warm water, then 
ground in a mill, and the product run into a large vat, where it is 
allowed to undergo lactic fermentation. During this process the 
sugar in the grain is converted into lactic, butyric, and acetic acids, 
and the gluten (see below) is brought into a less tenacious condition, 
which favours the subsequent washing of the starch, an opera- 
tion which is carried out in the manner described above. 

Starch is a white powder, which, when examined under the 



THE CARBOHYDRATES. 279 

microscope, is seen to be made up of peculiarly striated 
granules, having a definite shape and structure. Granules 
from different plants vary very much in appearance and in 
size, as shown below * (magnified 350 diameters), those 






Fig. 22. 

(a) Barley Starch ; (b) Potato Starch ; (c) Wheat Starch. 

composing potato starch being comparatively large, those 
of barley starch considerably smaller. 

Starch is insoluble in cold water, but when heated with 
water the granules swell up and then burst. The contents 
of the cells, or the granulose, dissolves, but the cell-wall, 
or starch cellulose, is insoluble, and can be separated by 
filtration; on adding alcohol to the filtrate the granulose 
* From The Microscope in the Brewery. 



280 THE CARBOHYDRATES. 

is precipitated as an amorphous powder which is known 
as soluble starch. 

The homogeneous, gelatinous mass obtained when starch is 
heated with water is called starch paste, and is largely used 
for stiffening linen and calico goods, and also as a substitute 
for gum. It is best prepared by rubbing starch into a thin 
paste with cold water, and then adding a considerable quantity 
of boiling water. 

Characteristic of starch is the brilliant blue colour which is 
produced when a solution of iodine is added to starch paste, 
and to its solution in water ; this colour disappears on heating, 
but reappears on cooling. 

When boiled with dilute acids, starch is first converted 
into dextrin (C 6 H 10 5 )ft, and then into glucose, 
(C 6 H 10 0> + wH 2 = wC 6 H 12 6 . 

Malt extract, containing the ferment, diastase, decomposes 
starch at 60-70, with formation of dextrin and maltose, 
3C 6 H 10 5 + H 2 = C 6 H 10 5 + C 12 H 22 O n , 

a process which, as already mentioned (p. 98), is of the utmost 
importance in the manufacture of alcohol and spirituous 
liquors from grain. 

The empirical formula of starch is C 6 H 10 5 ; the molecular 
formula has not as yet been determined, but as it is un- 
doubtedly many multiples of the empirical formula, it is 
usually expressed by (C 6 H 10 5 )w. 

Gluten. Wheaten flour contains about 70 per cent, of starch and 
10 per cent, of a sticky, nitrogenous substance called gluten. An 
approximate separation of these two constituents may be brought 
about by kneading flour in a thin calico bag under water, when the 
starch passes through with the water, forming a milky liquid, from 
which it is deposited on standing. The gluten remains in the bag 
as a tenacious, sticky, gray mass, which soon decomposes and 
smells disagreeably. 

Both starch and gluten are very valuable food-stuffs. 

Dextrin, (C 6 H 10 5 )rc, is the name given to the substance, 
or mixture of substances, obtained as an intermediate product 



THE CARBOHYDRATES. 281 

in the conversion of starch into glucose (see above). It is 
produced on heating starch to about 210, or on treating it 
with dilute acids or with malt extract. 

Dextrin is a colourless, amorphous substance, soluble in 
water, and is largely used as a cheap substitute for gum; 
when boiled with dilute acids it is converted into glucose. 
It is probably a mixture of various isomeric substances of 
the empirical formula C 6 H 10 5 . 

Cellulose, (C 6 H 10 6 )w, like starch, occurs very widely distri- 
buted throughout the vegetable kingdom. It is the principal 
constituent of cell membrane and of wood, and constitutes, 
indeed, the framework of all vegetable tissues. 

Linen, cotton-wool, hemp, and flax, which have been freed 
from inorganic matter by repeated extraction with acids, 
consist of almost pure cellulose j an even purer form may be 
obtained by extracting Swedish filter-paper with hydrofluoric 
acid, in order to remove traces of silica, washing well with 
water, and drying at 100. 

Cellulose is insoluble in all the ordinary solvents, but it dis- 
solves in an ammoniacal solution of cupric oxide (Schweitzer's 
reagent). It is reprecipitated from this solution on the 
addition of acids, in the form of a jelly, which, when washed 
with water and dried, is obtained in the form of an amorphous 
powder. 

Concentrated sulphuric acid gradually dissolves cellulose, 
and if the solution be diluted with water and boiled, dextrin 
and ultimately dextrose are produced. It is thus possible to 
convert wood into sugar, and indirectly into alcohol. 

If unsized paper be subjected to the action of sulphuric 
acid for a few seconds, then washed with water and dilute 
ammonia, and again with water, it is converted into a tough 
substance called parchment paper on account of its resem- 
blance to parchment. Such paper serves as a convenient 
substitute for animal membrane, and is used for a variety of 
purposes. 

Cellulose gives on analysis results agreeing with the formula 



282 THE CARBOHYDRATES. 

C 6 H 10 5 , but its molecular formula is certainly very much 
greater than this, and is therefore written (C 6 H 10 6 )?, or 
more frequently (C 12 H 20 10 )ft. 

When heated with acetic anhydride and a trace of zinc 
chloride, it yields cellulose decacetate, C 12 H 10 (0-CO-CH 3 ) 10 , 
a white flocculent mass, which is reconverted into cellulose 
by alkalies. 

Gun-Cotton, Cordite, and Collodion. When cotton-wool is 
treated with nitric acid, or, better, with a mixture of nitric 
and sulphuric acids, nitrates of cellulose of variable com- 
position are produced, according to the amount and con- 
centration of the acids employed, and the length of time 
during which they are allowed to act. 

If cotton-wool be soaked in ten parts of a mixture of one 
part of nitric acid (sp. gr. 1-5) and three parts of concentrated 
sulphuric acid for twenty-four hours, the resulting mass, after 
thoroughly washing and drying, constitutes gun-cotton. This 
substance has, approximately, the composition C 12 H 14 (N0 3 ) 6 4 , 
and is, therefore, cellulose hexa-nitrate. It is insoluble in a 
mixture of alcohol and ether. 

Gun-cotton burns rapidly and quietly, without smoke, when 
a flame is applied to it, but when fired with a detonator it 
explodes with great violence ; it is used as an explosive either 
alone or mixed with nitro-glycerin, the mixture being known 
as ballistite or blasting-gelatine. 

Cordite is a mixture of gun-cotton and nitro-glycerin, made 
into a gelatinous mass by the addition of acetone and vaseline, 
and then worked into threads; it is used as a smokeless 
powder. 

A mixture of gun-cotton with camphor constitutes the 
substance known as celluloid, which, although readily com- 
bustible, is not explosive. 

When treated with nitric and sulphuric acids for a short 
time only, cellulose is converted principally into tetm-nitrate, 
C 12 H 16 (N0 3 ) 4 6 , and penta-nitrate, C 12 H 15 (N0 3 ) 5 5 , both of 
which dissolve in a mixture of alcohol and ether ; a solution of 



THE CARBOHYDRATES. 283 

the mixed nitrates in alcohol and ether constitutes collodion, 
which is largely used for photographic and other purposes. 

The nitrates of cellulose are decomposed by alkalies, yield- 
ing nitrates of the alkalies and cellulose ; they are, therefore, 
true esters and not nitro-derivatives (p. 259). 

SUMMARY AND EXTENSION. 

The carbohydrates are usually subdivided into () the monoses ; 
(6) the biases ; (c) the polyoses. 

The monoses, as, for example, glucose, fructose, and galactose, 
have the composition C 6 H 12 6 . They all resemble glucose more 
or less closely in ordinary physical properties, reduce Fehling's 
solution, and usually undergo alcoholic fermentation with yeast ; 
they are not resolved into simpler substances on treatment with 
very dilute acids. 

The bioses, such as sucrose, lactose, and maltose, have the com- 
position C^H^OH. From their behaviour under various conditions, 
more especially with dilute mineral acids, they must be regarded 
as composed of 2 mols. of identical, or of different, monoses, less 
1 mol. of water that is to say, they are anhydride or ether-like 
derivatives of the monoses. Sucrose, for example, is an anhydride 
or ether-like substance formed from 1 mol. of glucose and 1 mol. of 
fructose, whereas lactose is derived from glucose and galactose in a 
similar manner. With the exception of maltose, the bioses are not, 
as a rule, directly fermentable with yeast (compare sucrose), nor do 
they immediately reduce Fehling's solution, as in both cases they 
must first be converted into monoses by hydrolysis. 

The polyoses, such as starch and cellulose, have the composition 
(C 6 H 10 O 5 )n, and are much more complex than the bioses, as is shown 
by their behaviour on hydrolysis; starch, for example, yields, 
under certain conditions, not only maltose, C^H^Ou, but also 
dextrin, a compound which has itself a very high molecular weight, 
so that the molecule of starch must be highly complex. The high 
molecular weight of the polyoses, compared with the monoses and 
bioses, is also indicated by their general physical properties, as, 
for example, their insolubility and their non-crystalline character. 
The polyoses do not ferment with yeast, and do not reduce Fehling's 
solution. 

The constitutions of the members of the carbohydrate group have 
been ascertained with certainty only in the case of some of the 
monoses. That the monoses are either aldehydes (aldoses) or 
ketones (ketoses) is shown by their behaviour on oxidation and 



284 THE CARBOHYDRATES. 

reduction, and also by the fact that they interact with phenyl- 
hydrazine, hydroxylamine, &c. ; that they contain hydroxyl-groups 
is proved by their conversion into acetyl-derivatives (and in the case 
of the polyose, cellulose, by its conversion into various nitrates). 

The constitutions of the monoses are further determined by a 
method which was worked out by Kiliani, and which is based on 
the following reactions : The monoses, like the simpler aldehydes 
and ketones, combine directly with hydrogen cyanide, forming 
cyanohydrins (p. 142), 

M-CHO + HCN = M-CH(OH)-CN 
M.COCH 2 .OH + HCN = M-C(OH)(CN)CH 2 OH, 
and these products are converted into polyhydric acids on hydro- 
lysis with a mineral acid, 

M-CH(OH)-CN + 2H 2 = M-CH(OH) COOH + NH 3 
M-C(OH)(CN)-CH 2 -OH + 2H 2 O = M-C(OH)(COOH).CH 2 -OH + NH 3 . 

When these polyhydric acids are heated at a high temperature 
with a large excess of hydriodic acid and a little amorphous 
phosphorus, all the hydroxyl-groups in the molecule are displaced 
by hydrogen atoms that is to say, complete reduction of all the 
>CH-OH and CH 2 -OH groups is effected, and a fatty acid is 
obtained. In the case of the polyhydric acid prepared from glucose 
cyanohydrin, this change is represented by the equation 
CH 2 (QH).[CH.OH] 4 .CH(OH).COOH + 12HI= 

CH 3 .[CH 2 ] 4 .CH 2 .COOH + 6H 3 O + 6I 2 , 

and normal heptylic acid is obtained ; whereas on reducing the 
corresponding polyhydric acid prepared from fructose cyanohydrin, 
methylbutylacetic acid, an isomeride of normal heptylic acid, is 
formed, 
CH 2 (OH).[CH.OH] 3 .C(OH)(COOH).CH 2 .OH + 12HI = 

CH 3 .[CH 2 ] 3 .CH(COOH).CH 3 + 6H 2 + 6I 2 . 

These facts show that glucose is an aldehyde and a derivative of 
normal hexane. Had it been a ketone, the polyhydric acid pro- 
duced from it could not have contained the group CH(OH)'COOH, 

but must have contained the group 



this, on reduction, would have been transformed into 



and consequently the fatty acid finally produced would not have 
been normal heptylic acid, but one of its isomerides. Obviously. 
also, the conversion of fructose into methylbutylacetic acid, taken 



CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 285 

in conjunction with other facts, shows that this sugar is a ketone 
and not an aldehyde, and that its constitution is expressed by the 
formula already given (p. 271). In addition to this evidence, the 
fact that glucose and fructose may be converted into secondary 
hexyl iodide (p. 265) shows them to be derivatives of normal 
hexane. 

Both galactose and mannose are aldehydes (aldoses), identical 
with glucose in constitution, but differing from the latter in optical 
and other properties (Part II. p. 555). 



CHAPTER XVI. 

CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 

The cyanogen compounds contain the monovalent radicle, 
cyanogen, -CiN (Gay-Lussac), and may be considered as 
derivatives of cyanogen, (GN) 2 ; in many respects they are 
closely related to the corresponding halogen derivatives, 
although they differ from the latter in composition, and con- 
tain the monovalent group of atoms CN in the place of a 
single atom of halogen, (-C1), as shown by the following 
examples, 

Cljj, HC1, KC1, AgCl, HgCl 2 , HO-C1, C 2 H 5 .C1 

(CN) 2 , HCN, KCN, AgCN, Hg(CN) 2 , HO-CN, C 2 H 5 -CK 
This fact brings out very clearly the meaning of the term 
' radicle,' the monovalent group -CN* playing much the 
same part as the atom of chlorine, just as the radicle ammo- 
nium may play the part of a single atom of an alkali metal. 

Cyanogen, dicyanogen, C 2 N 2 , Cy 2 , or N=C C=N, is pro- 
duced in small quantities when the electric arc passes between 
carbon poles in an atmosphere of nitrogen, 



also when ammonium oxalate is strongly heated with phos- 
phoric anhydride, 

NH 4 OOC-COONH 4 = N=C C=~N + 4H 2 0, 

* Cy is often used to represent the cyanogen radicle -ON, 



286 CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 

a reaction of considerable interest, as it shows that cyanogen 
is the nitrile (p. 289) of oxalic acid. 

A mixture of anhydrous ammonium oxalate and phosphoric 
anhydride is heated in a glass tuhe sealed at one end, and the 
products are collected in a solution of caustic potash (see below) ; 
the latter is then tested for cyanide (p. 291). 

Cyanogen is prepared* by heating silver cyanide or mercuric 
cyanide (p. 291) in a hard glass tube, the gas being collected 
over mercury, 



During the operation a considerable quantity of a brown 
amorphous substance, called paracyanogen, (CN)w, is pro- 
duced ; this compound is a polymeride of cyanogen, and when 
heated at a high temperature it is completely resolved into 
cyanogen gas, just as trioxymethylene (metaformaldehyde) is 
converted into formaldehyde under like conditions (p. 121). 

Cyanogen is also prepared by heating potassium cyanide 
with cupric sulphate in aqueous solution, the cupric cyanide 
which is first precipitated undergoing decomposition into 
cyanogen and cuprous cyanide (compare behaviour of potassium 
iodide with cupric sulphate), 

4KCN + 2CuS0 4 = (CN) 2 + 2CuCN + 2K 2 S0 4 . 

Cyanogen is a colourless gas, which condenses to a liquid 
at ordinary temperatures under a pressure of four atmos- 
pheres; it has a peculiar smell, is excessively poisonous, and 
burns with a characteristic purple or peach-coloured flame, 
yielding carbon dioxide and nitrogen. 

It is moderately soluble in water, readily in alcohol, but its 
aqueous solution soon decomposes, a brown amorphous pre- 
cipitate ('azulmic acid') being deposited; the solution then 
contains ammonium oxalate and other substances. 

When an aqueous solution of cyanogen is treated with 
acids or with alkalies, oxalic acid or an oxalate is produced, 
N=C C=N + 4H 2 = NH 4 OOC-COONH 4 , 

* Owing to the highly poisonous character of cyanogen and of many of its 
derivatives, great care should be observed in their preparation, 



CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 287 

this change being the reverse of that which occurs when 
ammonium oxalate is heated with phosphoric anhydride. 

All substances which contain the cyanogen group behave 
in a similar manner, and are converted on hydrolysis into 
carboxylic acids or their salts, amides being formed as 
intermediate products ; this is a most important general 
reaction. 

Cyanogen is readily absorbed by potash, potassium cyanide 
and cyanate being produced, 

C 2 N 2 + 2KOH = KCN + KOCN + H 2 0, 

just as potassium chloride and hypochlorite are formed when 
chlorine is led into potash, 

C1 2 + 2KOH = KC1 + KOC1 + H 2 0. 

Cyanogen chloride, CNC1, is formed by the action of chlorine on 
a solution of hydrogen cyanide, 

HCN + C1 2 =CNC1 + HC1. 

It is a colourless, very poisonous liquid, boils at 15-5, and readily 
undergoes spontaneous polymerisation, yielding cyan-uric chloride, 
C 3 N 3 C1 3 , a solid substance which melts at 146, and is decomposed 
by aqueous alkalies, yielding cyanuiic acid, 

C 3 N 3 C1 3 + 3H 2 O = C 3 N 3 (OH) 3 + 3HC1. 

Cyanuric acid is a crystalline tribasic acid ; on distillation it is 
converted into cyanic acid (p. 295). 

Hydrogen cyanide (hydrocyanic or prussic acid), H-CiN 
(or H-N1C), was discovered by Scheele, and is found in the 
free state in plants, sometimes in considerable quantities; 
more frequently it occurs in combination with glucose and 
benzaldehyde in the form of the glucoside* amygdalin 
(Part II. p. 418). Bitter almonds and cherry kernels contain 
this glucoside; when macerated and kept in contact with 
water, fermentation soon sets in, due to the presence of a 

* The term rjlucoside is applied to all those vegetable products which, 
on treatment with acids or alkalies, yield a sugar, or some closely allied 
carbohydrate, and one or more other substances (frequently phenols or 
aromatic aldehydes) as decomposition products (compare p. 298). 



288 CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 

ferment, emulsin, and the amygdalin is decomposed into 
hydrogen cyanide, benzaldehyde, and glucose, 

C 20 H 27 NO n + 2H 2 = C 7 H 6 + HCN + 2C 6 H 12 6 . 

Amygdalin. Benzaldehyde. Glucose. 

Hydrogen cyanide is formed when the silent electric discharge 
passes through a mixture of hydrogen and cyanogen, 



and also when ammonium formate is heated with phos- 
phoric anhydride, a change which is analogous to the forma- 
tion of cyanogen from ammonium oxalate, and which can 
be demonstrated in a similar manner (p. 286), 



2 0. 

Hydrocyanic acid is prepared by distilling potassium cyanide, 
or, more usually, potassium ferrocyanide, with dilute sulphuric 
acid, 

KCN + H 2 S0 4 = KHS0 4 + HCN 

2K 4 Fe(CN) 6 + 3H 2 S0 4 - 6HCN + FeK 2 Fe(CN) 6 + 3K 2 S0 4 ; 

Potassium Ferrocyanide. Ferrous Potassioferrocyanide. 

in the latter reaction, only half of the potassium ferrocyanide 
yields hydrogen cyanide. 

Powdered potassium ferrocyanide (10 parts) is mixed with con- 
centrated sulphuric acid (7 parts) previously diluted with water 
( 10-40 parts, according to the desired strength of the hydrocyanic 
acid), and the mixture is distilled from a retort connected with a 
condenser. The anhydrous acid may be prepared from the aqueous 
solution thus obtained by fractional distillation and dehydration 
over calcium chloride, but very special precautions must be taken 
to avoid accidents. 

Anhydrous hydrogen cyanide is a colourless liquid ; it boils 
at 26, and solidifies in a freezing mixture to colourless 
crystals, which melt at -14; it has an odour similar to that 
of oil of bitter almonds, and burns with a pale blue flame, 
with formation of carbon dioxide, water, and nitrogen. It is 
a terrible poison, very small quantities of the liquid or of its 
vapour being sufficient to cause death, 



CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 289 

Hydrogen cyanide dissolves readily in water, but the 
solution rapidly decomposes, with separation of a brown 
substance, and the liquid then contains ammonium formate 
and other compounds, 

HCN + 2H 2 = H-COONH 4 . 

This hydrolysis takes place only slowly if a trace of some 
mineral acid be present, more quickly if the solution be 
heated with mineral acids or alkalies. 

On reduction with nascent hydrogen, hydrogen cyanide is 
converted into methylamine, 



The constitution of hydrogen cyanide may be expressed by 
the formula H-C:N for the following reasons: The acid is 
produced from ammonium formate, by a change similar to 
that by which methyl cyanide is formed from ammonium 
acetate (p. 293), 



CH 3 .COONH 4 = CH 3 -CN + 2H 2 ; 

when heated with mineral acids it is converted into formic 
acid, just as methyl cyanide is converted into acetic acid, 

H.CN + 2H 2 o = H.COOH + NH S 

CH 3 -CN + 2H 2 - CHg-COOH + NH 3 . 

As, moreover, many facts show that the methyl group in 
methyl cyanide and in acetic acid is directly united with 
carbon, it would seem probable that the hydrogen atom in 
hydrogen cyanide is in a similar state of combination. 

In some respects, however, hydrogen cyanide behaves as if it 
had the constitution H-NIC; its silver salt, for example, seems 
to contain the metal directly united with nitrogen (compare p. 295). 

Hydrogen cyanide is sometimes called formonitrile, the nitrile 
of formic acid, or rather of ammonium formate, the name nitrile 
being given to those compounds which are derived from ammonium 
salts by the elimination of 2 mols. of water. 

Hydrocyanic acid is a feeble acid, and scarcely reddens blue 
litmus. It forms salts with the hydroxides (but not with the 
carbonates) of potassium, sodium, and many other metals ; the 

on. s 



290 CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 

alkali salts are decomposed by carbon dioxide with liberation 
of the acid, and this is the reason why potassium cyanide, for 
example, in contact with moist air, always smells of hydrogen 
cyanide. 

Potassium cyanide, KCN, may be obtained synthetically by 
gently heating potassium in cyanogen. It is prepared on a 
large scale by strongly heating potassium ferrocyanide alone, 
or with potassium carbonate, out of contact with the air, 

K 4 Fe(CT) 6 = 4KCN + FeC 2 + N 2 
K 4 Fe(CN) 6 + K 2 C0 3 = 5KCN + KCNO + C0 2 + Fe. 

After allowing to settle, the fused mass is run off from the iron 
carbide, or iron ; in the first process the separation is incomplete, 
and the product must be purified by dissolving it in alcohol or 
acetone and evaporating the filtered solution ; in the second process 
the product contains a considerable quantity of cyanate, part of 
which may be reduced to cyanide by adding powdered charcoal to 
the fused mixture. 

Sometimes a mixture of sodium and potassium cyanides is manu- 
factured by fusing potassium ferrocyanide with sodium. 

The pure salt may be prepared by passing hydrogen cyanide 
into alcoholic potash, and separating the crystals which are 
precipitated. 

Potassium cyanide crystallises in colourless plates, and is 
very readily soluble in water, but nearly insoluble in absolute 
alcohol ; it is excessively poisonous. 

Fused potassium cyanide is a powerful reducing agent ; it 
liberates the metals from many metallic oxides, being itself 
converted into potassium cyanate, 

KCN + PbO = KCNO + Pb, 

hence its use in analytical chemistry and in some metallurgical 
operations; it is also used in large quantities in extracting 
gold from poor ores and ' tailings ' by the MacArthur-Forrest 
cyanide process. 

An aqueous solution of potassium cyanide gives, with silver 
nitrate, a curdy white precipitate of silver cyanide, AgCN, 
which is insoluble in dilute acids, but soluble in ammonia 



CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 291 

and in potassium cyanide ; in the latter case, with formation 
of the soluble double salt, KAg(CN) 2 , which is used in electro- 
plating. Silver cyanide is thus very similar in its properties 
to silver chloride, from which, however, it differs in this, 
that when heated it is decomposed completely into silver and 
cyanogen, 



Mercuric cyanide, Hg(CN) 2 , is prepared by dissolving mer- 
curic oxide in hydrocyanic acid, 

HgO + 2HCN - Hg(CN) 2 + H 2 0. 

The solution, on evaporation, deposits the salt in colourless 
crystals, which are moderately soluble in water ; when strongly 
heated, the salt is decomposed into mercury and cyanogen. 

The detection of hydrocyanic acid or of a cyanide is usually 
based on the following tests : (a) The aqueous solution is 
made strongly alkaline with potash, a few drops of ferrous 
sulphate added, and the liquid warmed; potassium ferro- 
cyanide is thus formed (p. 292), and on acidifying and adding 
ferric chloride, a blue colouration or precipitate of Prussian 
blue is produced, (b) The solution is mixed with a few drops 
of very dilute ammonium sulphide, and evaporated to dry ness 
on a water-bath ; the residue contains ammonium thiocyanate, 
and on the addition of ferric chloride an intense blood-red 
colouration is produced. 

The cyanides of many of the metals, like many of the 
metallic chlorides, are capable of forming ' double salts ' with 
the compounds of other metals. Silver cyanide, for instance, 
is soluble in potassium cyanide, with which it forms a double 
salt of the composition AgK(CN) 2 ; the compound KAu(CN) 4 
may be obtained in a similar manner by dissolving auric 
cyanide, Au(CN) 3 , in potassium cyanide. These 'double 
salts ' crystallise unchanged from water, but are decomposed 
by mineral acids in the cold, with evolution of hydrogen 
cyanide. Like the soluble simple cyanides, they are exces- 
sively poisonous. 



292 CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 

In addition to these double salts, complex metallic cyanides 
of a different class are known, the most important of which 
are potassium ferrocyanide, K 4 Fe(CK") 6 , and potassium ferri- 
cyanide, K 3 Fe(CN) 6 . These salts are not poisonous, and are 
more stable than the double salts just referred to. On treat- 
ment with mineral acids, in the cold, they do not yield 
hydrogen cyanide, but hydrogen is substituted for one of the 
metals only, and an acid, such as hydroferrocyanic acid, is 
liberated, 

K 4 Fe(CN) 6 + 4HC1 = H 4 Fe(CN) 6 + 4KCL 

Potassium ferrocyanide, or yellow prussiate of potash, 
K 4 Fe(CN) 6 , is formed when ferrous hydrate is dissolved in 
potassium cyanide, 

6KCN + Fe(OH) 2 = K 4 Fe(CN) 6 + 2KOH. 
It is manufactured by fusing together in an iron pot 
nitrogenous animal refuse (horn-shavings, hair, blood, &c.), 
crude potashes (containing potassium carbonate), and iron 
borings. The product is extracted with hot water, the solu- 
tion filtered, and evaporated to crystallisation. 

Potassium ferrocyanide cannot he present in the melted mass, 
because it is decomposed at a high temperature (p. 290) ; it must, 
therefore, be formed when the product is extracted with water. 

Probably the melt contains iron, potassium cyanide, and ferrous 
sulphide (the latter having been produced by the action of the 
sulphur in the animal refuse on the iron) ; these substances would 
interact in the presence of water, yielding potassium ferrocyanide, 



Fe(CN) 2 + 4KCN = K 4 Fe(CN) 6 . 

Potassium ferrocyanide crystallises in lemon-yellow prisms, 
which contain 3 mols. of water of crystallisation j it is soluble 
in about 4 parts of water. When warmed with strong (90 
per cent.) sulphuric acid it gives carbon monoxide, 
K 4 Fe(CN) 6 + 6H 2 * + 6H 2 S0 4 = 

6CO + 2K 2 S0 4 + FeS0 4 + 3(NH 4 ) 2 S0 4 , 

* The water necessary for this decomposition is partly derived from the 
crystals of the salt, partly from the acid, which is not anhydrous. 



CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 293 

but when boiled with dilute sulphuric acid it gives hydrogen 
cyanide. 

Solutions of ferric salts in excess give with potassium 
ferrocyanide a precipitate of 'Prussian blue,' or ferric 
ferrocyanide, 

Fe 4 [Fe(CN) 6 ] 3 . 

Potassium ferricyanide, or red prussiate of potash, 
K 3 Fe(CN) 6 , is prepared by passing chlorine into a solution 
of potassium ferrocyanide until the liquid ceases to give a 
blue precipitate with ferric salts ; on evaporation, potassium 
ferricyanide separates out in dark-red crystals. 

The transformation of potassium ferrocyanide into ferricyanide 
is simply a process of oxidation, as other oxidising agents, such 
as nitric acid and lead peroxide, produce the same result; this 
change is easily understood if it be assumed that potassium ferro- 
cyanide is a compound of potassium cyanide and ferrous cyanide, 
4KCN + Fe(CN) 2 . On oxidation, the ferrous is converted into 
ferric cyanide, and potassium ferricyanide, which may be re- 
garded as a compound of potassium cyanide and ferric cyanide, 
3KCN + Fe(CN) 3 , is formed. 

Potassium ferricyanide gives, with ferrous salts, a precipitate 
of Turnbull's blue, or ferrous ferricyanide, Fe 3 [Fe(CN) 6 ] 2 ; it 
is employed as a mild oxidising agent, as in alkaline solution, 
in presence of an oxidisable substance, it is converted into 
potassium ferrocyanide, 

2K 3 Fe(CN) 6 + 2KOH = 2K 4 Fe(CN) 6 + H 2 + O. 

The nitriles, or alkyl cyanides, as the esters of hydrogen 
cyanide are termed, may be prepared by heating the alkyl 
halogen compounds with potassium cyanide, 

KCN + C 2 H 5 I = C 2 H 5 -CN + KI, 

or by distilling the ammonium salts, or the amides, of the 
fatty acids with some dehydrating agent, such as phosphorus 
pentoxide, 

CH 3 -COO]SrH 4 = CH 3 .CN + 2H 9 
C 2 H 5 .CONH 2 = C,H 5 -CN + H 2 0. 



294 CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 

They are also formed when afcfoximes are treated with acetyl 
chloride or acetic anhydride, 

CH 3 -CH :NOH = CHg-CN + H 2 O. 

The lower members of the series, such as methyl cyanide 
(b.p. 81) and ethyl cyanide (b.p. 97), are colourless liquids, 
possessing a strong but not disagreeable smell, and are 
readily soluble in water ; the higher members, as, for example, 
octyl cyanide, C 8 H 17 -CN, are almost insoluble in water. 

When boiled with acids or alkalies they are decomposed, 
with formation of fatty acids, the -CN group being converted 
into the -COOH group, 

CH 3 -CN + KOH + H 2 = CH 3 .COOK + KH 3 
C 2 H 5 -CN + HC1 + 2H 2 = C 2 H 5 -COOH + NH 4 C1. 
For this reason, and also because they may be obtained from 
the ammonium salts of the fatty acids, the nitriles are named 
after the acids which they yield on hydrolysis; methyl 
cyanide, CH 3 'CN, for example, is called acetonitrile ; ethyl 
cyanide, C 2 H 5 -CN, propionitrile, and so on. 

On reduction with zinc and sulphuric acid, or, better, with 
sodium and alcohol, the alkyl cyanides are converted into 
primary amines, a fact which shows that the alkyl group is 
directly united with carbon, 

CH 3 .CN + 4H = CH 3 .CH 2 .NH 2 . 

The isonitriles, carbylamines or isocyanides, are isomeric with 
the nitriles : they may be prepared by heating the alkyl halogen 
compounds with silver cyanide, 

C 2 H 5 I + A gN^C = C 2 H 5 N=C + Agl, 

and by treating primary amines with chloroform and alcoholic 
potash (p. 207), 

CH 3 .NH 2 + 3KOH + CHC1 3 - CH 3 -N=C + 3KC1 + 3H 2 O. 
The isonitriles or carbylamines are colourless liquids, sparingly 
soluble in water ; they have an almost unbearable odour and 
poisonous properties. 

They boil at lower temperatures than the isomeric cyanides ; 
methyl isonitrile, CH 3 -NC, for example, boils at 58 ; ethyl 
isonitrile, C 2 H 5 -NC, at 82. They differ from the nitriles, inasmuch 
as they are not decomposed by boiling alkalies ; they are, however, 



CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 295 

readily decomposed by dilute mineral acids, yielding formic acid 
and an amine, 

C 2 H 5 -NC + 2H 2 = H-COOH + C 2 H 5 -NH 2 . 

This behaviour is also totally different from that of the nitriles, 
and shows that the alkyl-grotip in the isonitriles is united with 
nitrogen and not with carbon that is to say, the nitriles are 
esters of a hydrogen cyanide, H-C N, whereas the isonitriles may 
be regarded as derivatives of an isomeride of the constitution 
HN=C. 

In order to explain the difference in the constitution of the 
products obtained by the action of alkyl halogen compounds on 
potassium and silver cyanide respectively, it is necessary to assume 
either that in the formation of silver cyanide from potassium 
cyanide by precipitation, intramolecular change (p. 302) has taken 
place, K-C=N yielding Ag-N==C, or that silver cyanide, Ag-C=N, 
first yields, with the alkyl halogen compound, an additive pro- 
duct, which is then decomposed, yielding the isonitrile, 



Ag-G=N + C 2 H 5 I = Ag-C i N< 5 = C=N.C 2 H 5 + Agl. 

Cyanic acid, HO-CN, is produced when cyarmric acid 
(p. 287) is heated, and the vapours condensed in a receiver, 
cooled in a freezing mixture, 

C 3 N 3 (OH) 3 = 3HO-CK 

It is a strongly acid, unstable liquid, and at temperatures 
above rapidly undergoes polymerisation into an opaque, 
porcelain-like mass called cyamelide. Its aqueous solution 
decomposes very rapidly into carbon dioxide and ammonia, 



and therefore the acid cannot be prepared by the decomposi- 
tion of its salts with mineral acids. 

Potassium cyanate, KO-CN (or KN:CO), is produced when 
potassium cyanide slowly oxidises in the air, and also when 
cyanogen chloride is dissolved in potash ; it is usually pre- 
pared by heating potassium cyanide (or ferrocyanide) with 
some readily reducible metallic oxide, such as litharge or 
red-lead, and then extracting the product with dilute alcohol, 



296 CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 

It is a colourless, crystalline powder, readily soluble in water 
and dilute alcohol, but insoluble in absolute alcohol; its 
aqueous solution rapidly decomposes with formation of 
ammonium and potassium carbonates, 

2KO-CN + 4H 2 = (NH 4 ) 2 C0 3 + K 2 C0 3 . 
"When a solution of this cyanate is mixed with ammonium 
sulphate and evaporated, urea is formed, ammonium cyanate, 
NH 4 OCN, being the intermediate product (p. 301). 

Constitution of Cyanic Acid. Although cyanic acid is a com- 
paratively simple substance, there is some doubt as to whether 
its constitution should be expressed by the formula HO-C:N or 
H-N:CO. The fact that it contains a hydrogen atom displaceable 
by metals, and the formation of potassium cyanate from cyanogen 
chloride, (Cl-C-N), point to the first formula; the following facts, 
however, point to the alternative constitution. 

When potassium cyanate is distilled with potassium ethyl 
sulphate, and when silver cyanate is digested with ethyl iodide, 
the ester, ethyl isocyanate, is formed ; the ethyl-group in this ester 
is directly united to nitrogen because when ethyl isocyanate is 
heated with potash it yields ethylamine (p. 205), 

C 2 H 5 -N :CO + 2KOH = C 2 H 5 -NH 2 + K 2 CO 3 . 

If then ethyl isocyanate he formed from the metallic cyanates by 
simple substitution, the latter must be regarded as derivatives of 
HN:CO, 

K(C 2 H 5 )S0 4 + KN-CO = C 2 H 5 -N:CO + K 2 SO 4 

C 2 H 5 I + AgN-CO = C 2 H 5 -N:CO + Agl ; 

on the other hand, it is possible that additive compounds are first 
produced and then decomposed as follows, 



The alkyl isocyanates, of which ethyl isocyanate is an example, are 
unpleasant-smelling, volatile liquids, and were discovered by Wttrtz. 

Thiocyanic acid, or sulphocyanic acid, HS-CIST, is obtained 
in the form of its salts when the alkali cyanides are heated 
with sulphur, 



the change being analogous to the formation of cyanates by 
the oxidation of cyanides. 

Thiocyanic acid may be obtained by distilling potassium 



CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 297 

thiocyanate with dilute sulphuric acid; it is a liquid, 
solidifies at 12-5, and has a very penetrating odour. It is 
decomposed by moderately concentrated sulphuric acid, with 
evolution of carbon oxysulphide, 



Potassium thiocyanate, KS-CN, is prepared by fusing 
potassium cyanide (or ferrocyanide) with sulphur, and 
extracting the mass with alcohol. On concentrating the 
alcoholic solution, the salt is deposited in colourless, very 
deliquescent needles. The ammonium salt, NH 4 S-CN, is 
most conveniently prepared by warming alcoholic ammonia 
with carbon disulphide, 

4NH 3 + CS 2 = NH 4 S-CN + (NH 4 ) 2 S. 

The thiocyanates are used in inorganic analysis, as reagents 
for ferric salts, with which they give an intense blood-red 
colouration, caused by the formation of a double salt. 
Thiocyanates are also employed in dyeing and calico-printing 
as mordants, and are known commercially as 'rhodanates.' 

Potassium ferrocyanide and various sulphocyanides are now 
manufactured from ' spent oxide, ' the substance obtained in purify- 
ing coal-gas from hydrogen sulphide, by passing it through layers 
of ferric hydrate. Spent oxide contains Prussian blue (ferric ferro- 
cyanide), ammonium sulphocyanide, and other ammonium salts, 
together with a large quantity of sulphur. It is first extracted 
with water and the ammonium sulphocyanide separated from the 
solution by fractional crystallisation, or the solution is treated with 
copper sulphate and sulphur dioxide, when cuprous sulphocyanide, 
CuS-CN, is precipitated; this salt is then reconverted into the 
ammonium salt by decomposing it with ammonium sulphide. 
Ammonium sulphocyanide is also obtained from * gas-liquor ' by 
precipitating as cuprous salt and then proceeding as before. 

The damp spent oxide, which has been extracted with water, is 
heated with quicklime in closed vessels by means of steam, in 
order to convert the ferric ferrocyanide into ferric hydrate and 
soluble calcium ferrocyanide, 

Fe 4 [Fe(CN) 6 ] 3 -f-6Ca(OH) 2 =4Fe(OH) 3 + 3Ca. 2 Fe(CN) 6 , 
and the latter is then extracted with water, the residue being used 
as a source of sulphur in the manufacture of sulphuric acid. The 



298 CYANOGEN COMPOUNDS AND THEIR DERIVATIVES. 

solution of the calcium salt is next treated with the proper quantity 
of potassium chloride to form the very sparingly soluble potassium 
calcium ferrocyanide, K 2 CaFe(CN) 6 , which is separated, and finally 
converted into potassium ferrocyanide by boiling it with potassium 
carbonate ; the solution is filtered from calcium carbonate and 
evaporated. 

Alkyl thiocyanates are produced by distilling the alkyl iodides 
with potassium thiocyanate, or from the mercaptides (especially 
lead mercaptide), by the action of cyanogen chloride, 

(C 2 H 5 S) 2 Pb + 2C1CN = 2C 2 H 5 S-CN + PbCl 2 . 

They are volatile liquids possessing a slight smell of garlic ; when 
oxidised with nitric acid they are converted into alkyl sulphonic 
acids, C 2 H 5 S-CN, for example, yielding C 2 H 5 -SO 3 H, a reaction which 
shows that the alkyl-group is united with sulphur, and that the 
esters are derived from an acid of the constitution HS-C N. 

Tiheal/cyl isothiocyanates, or mustard-oils, are produced by heating 
the normal thiocyanates at 180, or by simply repeatedly distilling 
them, intramolecular change (p. 302) taking place, 

C 2 H 5 .S-C;N > S:C:N-C 2 H 5 ; 

the alkyl-group in these compounds is combined with nitrogen, as 
shown by the fact that when heated with hydrochloric acid they are 
decomposed into primary amines, carbon dioxide, and sulphuretted 
hydrogen, 

C 2 H 5 N :CS + 2H 2 O = C 2 H 5 .NH 2 + CO 2 + SH 2 . 

The isothiocyanates are therefore analogous to the alkyl isocyanates, 
and are derived from an unknown isothiocyanic acid of the con- 
stitution HN:C:S. 



Allyl isothiocyanate, or 'mustard oil,' C 

is prepared by distilling macerated black mustard seeds with 
steam. Mustard seeds contain a glucoside, 'potassium 
myronate,' C 10 H 18 NS 2 10 K, which is soluble in water; its 
solution gradually undergoes fermentation (owing to the 
presence of an enzyme, ' myrosin '), mustard-oil, glucose, and 
potassium hydrogen sulphate being produced, 

C 10 H 18 NS 2 10 K = C 3 H 5 -N:CS + C 6 H 12 6 + KHS0 4 . 
Allyl isothiocyanate may be obtained synthetically by heating 
allyl iodide with potassium thiocyanate (see above) ; it is a 
colourless, pungent-smelling liquid, boiling at 151; when 
dropped on the skin it produces blisters. 



AMIDO-ACIDS AND THEIR DERIVATIVES. 299 

CHAPTER XVII. 

AMIDO-ACIDS AND THEIR DERIVATIVES. 

Two classes of compounds containing the amido-group, 
-NH 2 , have already been described namely, the amides, 
such as acetamide, CH 3 -CO-NH 2 (p. 164), and the primary 
amines, such as ethylamine, C 2 H 5 -NH 2 (p. 205). In the 
former, the amido-group is easily separated from the rest of 
the molecule, inasmuch as all amides are hydrolysed more or 
less rapidly by boiling aqueous alkalies, giving ammonia and 
an alkali salt of the acid ; in the latter, however, the amido- 
(or amino-) group resists the action of alkalies and can only 
be removed by the action of nitrous acid (p. 207). Another 
important difference between these two classes of compounds 
is that, whereas the amines are strongly basic and form 
very stable salts, the amides are only very weak bases 
and, although they form salts with strong acids, their salts 
are very unstable ; for this reason and because they show a 
neutral reaction to litmus, amides are not generally regarded 
as bases. 

These facts afford a good illustration of the manner in which 
the properties of a given group may be modified by the other 
atoms or groups in the molecule. 

Now, just as the halogen atom in an alkyl halogen com- 
pound or in an acid chloride may be displaced by the amido- 
group, so may the halogen atom of a substituted acid 
such as chloracetic acid ; when, for example, chloracetic acid 
(p. 166) is dissolved in concentrated ammonia at ordinary 
temperatures, it is converted into the ammonium salt of 
amido-acetic acid, 

CH 2 C1-COOH + 3NH 4 -OH - NH 2 -CH 2 .COONH 4 + NH 4 C1 
+ 3H 2 0. 

Glycine, or amido-acetic acid, CH 2 (NH 2 )-COOH, can be 



300 AMIDO-ACIDS AND THEIR DERIVATIVES. 

prepared from this ammonium salt as described below ; it 
is found in certain animal secretions, usually in combination. 
As hippuric add or benzoylglycine, C 6 H 5 -CO-NH-CH 2 'COOH 
(Part II. p. 430), it occurs in considerable quantities in the 
urine of horses, and it may be prepared by heating hippuric 
acid with hydrochloric acid, 

C 6 H 5 .CO.NH.CH 2 .COOH + H 2 + HC1 - 

C 6 H 5 .COOH + NH 2 .CH 2 .COOH, HC1. 

Benzoic Acid. Glycine Hydrochloride. 

Glycine crystallises from water in colourless prisms, and 
melts at about 235 ; it has a sweet taste, is readily soluble 
in water, and its aqueous solution gives with ferric chloride a 
deep-red colouration. 

Glycine contains a carboxyl-group, and has, therefore, the 
properties of an acid; but it also contains an amido-group, 
which, like that in methylamine, H-CH 2 -NH 2 , confers basic 
properties. The result is that glycine is neutral to litmus, but 
is capable of forming salts with bases or with acids. 

The most characteristic metallic salt is the copper salt, 
which is readily formed by boiling cupric hydrate with a hot, 
strong aqueous solution of the acid or of its ammonium salt, 

2NH 2 .CH 2 .COONH 4 + Cu(OH) 2 - (NH 2 .CH 2 .COO) 2 Cu 



on cooling, the copper salt crystallises in deep-blue needles. 
The acid is easily obtained from this salt by passing hydrogen 
sulphide into its aqueous solution, filtering from copper 
sulphide, and evaporating. 

Glycine hydrochloride, C 2 H 5 N0 2 , HC1, is produced by dis- 
solving glycine in hydrochloric acid, or by decomposing hip- 
puric acid with hydrochloric acid ; it crystallises in colourless 
needles, and is readily soluble in water. 

Towards nitrous acid glycine behaves like a primary amine, 
its amido-group being displaced by hydroxyl (p. 207), with 
formation of glycollic acid (p. 229), 

CH 2 (NH 2 )-COOH + ff 2 H = CH 2 (OH)-COOH + N 2 + H 2 0. 



AMIDO-ACTDS AND THEIR DERIVATIVES. 301 

Other amido-acids, such as alanine or a-amicloprop ionic 
acid, CH 3 .CH(NH 2 ).COOH, may be prepared from the cor- 
responding halogen acids by the action of ammonia ; they are 
very similar to glycine in chemical properties, and when treated 
with nitrous acid they yield the corresponding hydroxy- 
acids (p. 232). 

Amido-formic acid or carbamic acid, NH 2 -COOH, is known only in 
the form of its ammonium and alkyl salts. Its ammonium salt, 
NH 2 -COONH 4 , is produced by the direct combination of carbon 
dioxide and ammonia, and is one of the constituents of commercial 
ammonium carbonate ; it is usually called ammonium carbamate. 

The esters of amido-formic acid are termed urethanes (because 
of their relation to urea) or alkyl carbamates. 

Urethane or ethyl carbamate, NH 2 -COOC 2 H 5 , may be prepared 
by treating ethyl carbonate (compare foot-note p. 177) or ethyl 
chloroformate with ammonia at ordinary temperatures, 

OH 



It is a volatile crystalline compound melting at 50, and when 
heated with ammonia it is converted into urea, 

' 



Urea, or carbamide, CH 4 N" 2 or CO(NH 2 ) 2 , is a compound 
of great physiological importance. It occurs in the urine of 
mammals and of carnivorous birds and reptiles, and is one 
of the principal nitrogenous constituents of human urine, of 
which it forms about 3 per cent. 

It was discovered in urine in 1773, and was first artificially 
produced in 1828 by Wohler, who found that on warming 
an aqueous solution of ammonium cyanate the salt was con- 
verted into urea, a discovery which, having led to the first 
synthetical production of an animal product, was of funda- 
mental importance (compare p. 2). 

Ammonium cyanate and urea are isomeric that is to say, 
they have the same molecular formula, CON 2 H 4 , but the 
atoms in the molecules of the two compounds are arranged 



302 AMIDO-ACIDS AND THEIR DERIVATIVES. 

differently their constitutions are different; the conversion 
of the one into the other is called an infra-molecular change 
because it merely involves a rearrangement of the atoms 
within the molecule, NH 4 -0-C:N (or NH 4 -N:C:0) being 
transformed into NH 2 -CO-NH >2 . 

Urea may be prepared from urine by evaporating to a small bulk 
and adding strong nitric acid. The precipitate of crude urea nitrate 
(see below) is recrystallised from nitric acid, dissolved in boiling 
water, and decomposed with barium carbonate; the solution is 
then evaporated to dryness, and the urea extracted with alcohol, 
in which barium nitrate is insoluble. 

It is more commonly prepared by mixing a solution of potassium 
cyanate (2 mols.) with an equivalent quantity of ammonium sulphate 
(1 mol.), evaporating to dryness, and extracting with alcohol. In 
both cases the crude urea is purified by recrystallisation from water 
or alcohol. 

Urea may also be obtained synthetically by treating ethyl 
carbonate, or carbonyl chloride* (phosgene gas), with ammonia, 
CO(OC 2 H 5 ) 2 + 2NH 3 = CO(NH 2 ) 2 + 2C 2 H 5 -OH 

COC1 2 + 4NH 3 = CO(NH 2 ) 2 + 2NH 4 C1. 
It crystallises in colourless needles, melts at 132, and 
is readily soluble in water and alcohol, but almost insoluble 
in ether; when heated with water at 120, or boiled with 
dilute acids, it is decomposed into carbon dioxide and ammonia 
(or one of its salts), 

CO(NH 2 ) 2 + H 2 + 2HC1 = C0 2 + 2NH 4 C1, 
but when heated alone it yields ammonia, cyanuric acid, 
biuret, and other compounds. 
Biuret is obtained when urea is heated at about 155, 
2NH 2 CO NH 2 =NH 2 .CO.NH.CO.NH 2 +NH 3 ; 
on dissolving the residue in water and adding first a drop of copper 
sulphate solution, and then excess of potash, a violet or red coloura- 
tion is produced. 

* Carbonyl chloride is obtained by the direct combination of carbon 
monoxide and chlorine in sunlight ; it is a gas which decomposes rapidly in 
contact with water, into carbon dioxide and hydrochloric acid, and when 
treated with alcohol it gives ethyl chloroformate, C1-CO-OC 2 H 5 , and ethyl 
carbonate (compare foot-note, p. 177). 



AMIDO-ACIDS AND THEIR DERIVATIVES. 303 

Urea is decomposed by nitrous acid, giving nitrogen, carbon 
dioxide, and water, the amido-groups being displaced by 
hydroxyl-groups, 
CO(NH 2 ) 2 + 2HN0 2 - CO(OH) 2 {C0 2 + H 2 0} + 2N 2 + 2H 2 ; 

a similar change takes place when urea is treated with 
solutions of hypochlorites or hypobromites, 

CO(NH 2 ) 2 + SNaOCl = C0 2 + N 2 + 2H 2 + SffaCl, 

and by measuring the volume of nitrogen given off, the 
quantity of urea can be readily estimated. 

Urea possesses basic properties, and combines with one 
equivalent of an acid to form salts, most of which are soluble 
in water. The most characteristic salt is urea nitrate, 
CO(NH 2 ) 2 ,HN0 3 , which crystallises in glistening plates, and 
is sparingly soluble in nitric acid. 

Constitution. The formation of urea from ethyl carbonate 
and from the chloride of carbonic acid (carbonyl chloride) are 
reactions analogous to those which take place in the formation 
of acetamide from ethyl acetate and from acetyl chloride ; urea 

may therefore be represented by the formula C0<^ fl - 2 , and 

regarded as the diamide of carbonic acid hence the name 
carbamide. 

Carbonyl chloride may also be regarded as the acid chloride, 
C1-COC1, of chloroformic acid, Cl-COOH, and urea as the amide of 
amidoformic acid. 

Uric acid, C 5 H 4 N 4 3 , occurs in small quantities in human 
urine, from which it separates on exposure to the air in 
the form of a light yellow powder ; sometimes it gradually 
accumulates in the bladder, forming large masses (stones), or is 
deposited in the tissues of the body (gout and rheumatism). 
It occurs in large quantities in the excrements of birds (guano) 
and reptiles. 

The excrements of serpents consist principally of ammonium 
urate, and uric acid is conveniently prepared by boiling the excre- 
ment with caustic soda until all the ammonia has been expelled, 



304 AMIDO-ACIDS AND THEIR DERIVATIVES. 

and then pouring the hot filtered liquid into hydrochloric acid ; on 
cooling, uric acid separates as a fine crystalline powder. 

Uric acid is insoluble in alcohol and ether, and very 
sparingly soluble in water (1 part dissolves in 1800 parts of 
water at 100). If uric acid be moistened with nitric acid 
in a porcelain basin, and the mixture then evaporated to 
dryness on a water-bath, a yellow stain is left, which, on the 
addition of ammonia, becomes intensely violet (murexide 
reaction). 

Uric acid is a weak dibasic acid ; when dissolved in sodium 
carbonate it yields an acid sodium salt, C 5 H 3 N 4 3 Na + JH 2 ; 
the normal sodium salt, C 5 H 2 N 4 3 Na 2 + H 2 0, is formed when 
uric acid is dissolved in caustic soda. The metallic salts, like 
the acid itself, are all very sparingly soluble in water. 

Uric acid has been prepared synthetically by heating 
glycine with urea, and by other methods. 



ORGANIC CHEMISTRY. 



PART II. 



CHAPTER XVIII. 

MANUFACTURE, PURIFICATION, AND PROPERTIES OF BENZENE. 

Distillation of Coal-tar. When coal is strongly heated 
out of contact with air, it undergoes very complex changes, 
and yields a great variety of gaseous, liquid, and solid volatile 
products, together with a non-volatile residue of coke. This 
process of dry or destructive distillation is carried out on the 
large scale in the manufacture of coal-gas, for which purpose 
the coal is heated in clay or iron retorts, provided with air- 
tight doors ; the gas and other volatile products escape from 
the retort through a pipe, and when distillation is at an end, 
the coke, a porous mass of impure carbon, containing the ash 
or mineral matter of the coal, is withdrawn. 

The hot coal-gas passes first through a series of pipes or 
condensers, kept cool by immersion in water or simply by 
exposure to the air, and, as its temperature falls, it deposits a 
considerable quantity of tar and gas-liquor, which are run 
together into a large tank; the gas is then forced through, 
or sprayed with, water, in washers and scrubbers, and, after 
having been further freed from tar, ammonia, carbon dioxide, 
and hydrogen sulphide by suitable processes of purification, 
it is led into the gas-holder and used for illuminating 

Org. Chem. T 



306 MANUFACTURE, PURIFICATION, 

and heating purposes. The average volume percentage com- 
position of purified coal-gas is H 2 = 47,CH 4 = 36,CO = 8,CO 2 
= 1,N 2 4, and hydrocarbons, other than marsh-gas (acety- 
lene, ethylene, benzene, &c.) = 4, but its composition is very 
variable. 

The coal-tar and the gas-liquor in the tank separate into 
two layers ; the upper one consists of gas-liquor or ammoniacal- 
liquor (a yellow, unpleasant-smelling, aqueous solution of am- 
monium carbonate, ammonium sulphide, and numerous other 
compounds), from which practically the whole of the ammonia 
and ammonium salts of commerce are obtained. The lower 
layer in the tank is a dark, thick, oily liquid of sp. gr. 1-1 to 
12, known as coal-tar. It is a mixture of a great number 
of organic compounds, and, although not long ago it was 
considered to be an obnoxious by-product, it is now the 
sole source of very many substances of great industrial 
importance. 

In order to partially separate the several constituents, the 
tar is submitted to fractional distillation ; it is heated in large 
wrought-iron stills or retorts, and the vapours which pass off 
are condensed in long iron or lead worms immersed in water, 
the liquid distillate being collected in fractions. The point 
at which the receiver is changed is ascertained by means of 
a thermometer which dips into the tar, as well as by the 
character of the distillate. 

In this way the tar is roughly separated into the following 
fractions : 

I. Light oil or crude naphtha Collected up to 170. 

IT. Middle oil or carbolic oil between 170 and 230. 

III. Heavy oil or creosote oil ,. it 230 270. 

IV. Anthracene oil n above 270 Q . 

V. Pitch Residue in the still. 

I. The first crude fraction separates into two layers namely, 
gas-liquor (which the tar always retains mechanically to some 
extent) and an oil which is lighter than water, its sp. gr. 
being about 0-975, hence the name, light oil. This oil is 



AND PROPERTIES OF BENZENE. 307 

first redistilled from a smaller iron retort and the distillate 
collected in three principal portions, passing over between 
82-110, 110-140, and 140-170 respectively. All these 
fractions consist principally of hydrocarbons, but contain basic 
substances, such as pyridine, acid substances, such as phenol 
or carbolic acid, and various other impurities; they are, 
therefore, separately agitated, first with concentrated sulphuric 
acid, which dissolves out the basic substances, and then with 
caustic soda, which removes the phenols (p. 398), being washed 
with water after each treatment ; afterwards they are again 
distilled. The oil obtained in this way from the fraction 
collected between 82 and 110 consists principally of the 
hydrocarbons benzene and toluene, and is sold as '90 per 
cent, benzol;' that obtained from the fraction 110-140 
consists essentially of the same two hydrocarbons (but in 
different proportions) together with xylene, and is sold as 
' 50 per cent, benzol.' * These two products are not usually 
further treated by the tar-distiller, but are worked up in 
the manner described later. The oil from the fraction col- 
lected between 140-170 consists of xylene, pseudocumene, 
mesitylene, &c., and is principally employed as 'solvent 
naphtha,' also as ' burning naphtha.' 

II. The second crude fraction, or middle oil, collected 
between 170 and 230, has a sp. gr. of about 1-002, and con- 
sists principally of naphthalene and carbolic acid. On cooling, 
the naphthalene separates in crystals, which are drained and 
pressed to squeeze out adhering carbolic acid and other sub- 
stances; the crude crystalline product is further purified by 
treatment with caustic soda and sulphuric acid successively, 
and finally sublimed or distilled. The oil from which the 
crystals have been separated is agitated with warm caustic 

* Commercial '90 per cent, benzol' contains about 70 per cent., and '50 
per cent, benzol' about 46 per cent., of pure benzene; the terms refer to 
the proportion of the mixture which passes over below 100 when the com- 
mercial product is distilled. Benzene, toluene, and xylene are known 
commercially as benzol, toluol, and xylol respectively. 



308 MANUFACTURE, PURIFICATION, 

soda to dissolve the carbolic acid ; the alkaline solution is 
then drawn off from the insoluble portions of the oil and 
treated with sulphuric acid, whereupon crude carbolic acid 
separates as an oil, which is washed with water and again 
distilled ; it is thus separated into crystalline (pure) carbolic 
acid and liquid (impure) carbolic acid. 

III. The third crude fraction, collected between 230 and 
270, is a greenish-yellow, fluorescent oil, specifically heavier 
than water; it contains carbolic acid, cresol, naphthalene, 
anthracene, and other substances, and is chiefly employed 
under the name of 'creosote oil' for the preservation of 
timber. 

IV. The fourth crude fraction, collected at 270 and 
upwards, consists of anthracene, phenanthrene, and other 
hydrocarbons which are solid at ordinary temperatures; the 
crystals which are deposited on cooling, after having been 
freed from oil by pressure, contain about 30 per cent, of 
anthracene, and are further purified by digestion with solvent 
naphtha, which dissolves the other hydrocarbons more readily 
than the anthracene ; the product is then sold as * 50 per 
cent, anthracene,' and is employed in the manufacture of 
alizarin dyes. The oil drained from the anthracene is redis- 
tilled, to obtain a further quantity of the crystalline product, 
the non-cry stallisable portions being known as ' anthracene 

on; 

Y. The pitch in the still is run out while still hot, and is 
employed in the preparation of varnishes, for protecting wood 
and metal work, and in making asphalt. 

The table (p. 309), taken partly from Ost's Lehrbuch der 
teclmischen Chemie, shows in a condensed form the process 
of tar distillation and the more important commercial products 
obtained. 

Benzene, C 6 H 6 . The crude ' 90 per cent, benzol ' of the 
tar-distiller consists essentially of a mixture of benzene and 
toluene, but contains small quantities of xylene and other 
substances ; on further fractional distillation in specially 



AND PROPERTIES OF BENZENE. 



309 



, 
to 



RACENE 
ove 270 
arate 



-ill 



-27 
te. 



3 



i 

-2 



s g 

tl , 

3 II II 

W _32 < -o * 



0* 



& - 



rf.3 >> 

llUli i 
- a f l^lllf ^ 

O e 








b 


O 


+ rt 
|| 


ii 




~| 


3<-3 


if 


S"i, 

O cj 






S '^3-3 


MS 


M g 


ll 


^ 


HI 


^ 

ss 


h 


i 


| 


111 


1" 


r 


H 




>>"= s 


. 


i 


3 


b 


ir 

w 


1 


Pi 



310 MANUFACTURE, PURIFICATION, 

constructed apparatus, it is separated more or less com- 
pletely into its constituents. The benzene prepared in this 
way still contains small quantities of toluene, paraffins, carbon 
disulphide, and other impurities, and may be further 
treated in the following manner : It is first cooled in a freez- 
ing mixture and the crystals of benzene quickly separated 
by filtration from the mother-liquor, which contains most of 
the impurities ; after repeating this process, the benzene is 
carefully distilled, and the portion boiling at 80-81 collected 
separately. 

For ordinary purposes this purification is sufficient, but even now 
the benzene is not quite pure, and, when it is shaken with cold 
concentrated sulphuric acid, the latter darkens in colour owing to 
its having charred and dissolved the impurities ; pure benzene, on 
the other hand, does not char with sulphuric acid, so that if the 
impure liquid he repeatedly shaken with small quantities of the 
acid, until the latter ceases to be discoloured, most of the foreign 
substances will Le removed. 

All coal-tar benzene which has not been purified in this way 
contains an interesting sulphur compound, C 4 H 4 S, named thiophene, 
which was discovered by V. Meyer ; the presence of this substance 
is readily detected by shaking the sample with a little concentrated 
sulphuric acid arid a trace of isatin (an oxidation product of indigo), 
when the acid assumes a beautiful blue colour (iudophenin reac- 
tion) ; thiopheue resembles benzene very closely in chemical and 
physical properties, and for this reason cannot be separated from it 
except by repeated treatment with sulphuric acid, which dissolves 
thiophene more readily than it does the hydrocarbon. 

Although the whole of the benzene of commerce (* benzol ') 
is prepared from coal-tar, the hydrocarbon is also present in 
small quantities in wood-tar and in the tarry distillate of 
many other substances, such as shale, peat, &c. ; it may, in 
fact, be produced by passing the vapour of alcohol, ether, 
petroleum, or of many other organic substances through a 
red-hot tube, because under these conditions such compounds 
lose hydrogen (and oxygen), and are converted into benzene 
and its derivatives. 

Benzene may be produced synthetically by simply heating 



AND PROPERTIES OF BENZENE. 



311 



acetylene at a dull-red heat, when 3 mols. (or 6 vols.) of the 
latter are converted into 1 niol. (or 2 vols.) of benzene, 



Acetylene (Part I. p. 81) is collected over mercury in a piece of 
hard glass-tubing, closed 
at one end and bent at 
an angle of about 120 ; 
when the tube is about 
half-full of gas, the lower 
end is closed with a cork, 
and a piece of copper 
gauze wrapped round a 
portion of the horizontal 
limb, as shown (fig. 23). 
This portion of the tube 
is then carefully heated 
with a Bunsen burner, 
the other end remaining 
immersed in the mercury ; 
after a short time vapours 
appear in the tube, and 
minute drops of benzene 
condense on the sides, 
and if, after heating for 
about fifteen minutes, 
the tube be allowed to Fig. 23. 

cool and the cork then 

removed, the mercury will rise, showing that a diminution in 
volume has taken place. 

This conversion of acetylene into benzene is a process of poly- 
merisation, and was first accomplished by Berthelot. It is, at 
the same time, an exceedingly important synthesis of benzene 
from its elements, because acetylene may be obtained by the 
direct combination of carbon and hydrogen (Part I. p. 81). 

Pure benzene may be conveniently prepared in small 
quantities by heating pure benzoic acid or calcium benzoate 
with soda-lime, a reaction which recalls the formation of 
marsh-gas from calcium acetate, 

(C 6 H 5 -COO) 9 Ca + 2NaOH = 2C 6 H 6 + CaC0 3 + Na 2 C0 3 , 
or C 6 H 5 .COOH = C 6 H 6 + CO,, 







312 MANUFACTURE, PURIFICATION, 

The analysis of pure benzene shows that it consists of 
92-31 per cent, of carbon and 6-69 per cent, of hydrogen, 
a result which gives the empirical formula CH ; the vapour 
density of benzene, however, is 39, so that its molecular 
weight is 78, which corresponds witli the molecular formula 
C 6 H 6 . 

At ordinary temperatures benzene is a colourless, highly 
refractive, mobile liquid of sp. gr. 0-8799 at 20, but when 
cooled in a freezing mixture it solidifies to a crystalline mass, 
melting again at 5-4, and boiling at 80-5. It has a burning 
taste, a peculiar, not unpleasant smell, and is highly inflam- 
mable, burning with a luminous, very smoky flame, which is 
indicative of its richness in carbon ; the luminosity of an 
ordinary coal-gas flame is, in fact, largely due to the presence 
of benzene. Although practically insoluble in water, benzene 
mixes with liquids such as ether and petroleum in all pro- 
portions; like the latter, it readily dissolves fats, resins, 
iodine, and other substances which are insoluble in water, 
and is for this reason extensively used as a solvent and 
for cleaning purposes ; its principal use, however, is for 
the manufacture of nitrobenzene (p. 365) and other benzene 
derivatives. 

Benzene is a very stable substance, and is resolved into 
simpler substances only with great difficulty; when boiled 
with concentrated alkalies, for example, it undergoes no 
change, and even when heated with solutions of such 
powerful oxidising agents as chromic acid or potassium per- 
manganate, it is only very slowly attacked and decomposed, 
carbon dioxide, water, and traces of other substances being 
formed. Under certain conditions, however, benzene readily 
yields substitution products ; concentrated nitric acid, even at 
ordinary temperatures, converts the hydrocarbon into nitro- 
benzene by the substitution of the inonovalent nitro-group 
-N0 2 for an atom of hydrogen, 

C 6 H 6 + HN0 3 m C 6 H 5 -N0 2 + H 2 0, 
and concentrated sulphuric acid, slowly at ordinary tempera- 



AND PROPERTIES OF BENZENE. 313 

turcs, but more rapidly on heating, transforms it into benzene- 
sulphonlc acid, 

C 6 H 6 + H 2 S0 4 = C 6 H 5 -S0 3 H + H 2 0. 

The action of chlorine and bromine on benzene is very 
remarkable : at moderately high temperatures, or in presence 
of direct sunlight, the hydrocarbon is rapidly converted into 
additive products, such as benzene hexachloride, C 6 H 6 C1 6 , 
and benzene hexabromide, C 6 H 6 Br 6 , by direct combination 
with six (but never more than six) atoms of the halogen ; 
in absence of sunlight and at ordinary temperatures, how- 
ever, the hydrocarbon is only slowly attacked, yielding 
substitution products, such as chlorobenzene, C 6 H 5 C1, bromo- 
benzene, C 6 H 5 Br, dichlorobenzene, C 6 H 4 C1 2 , &c. ; when, 
again, some halogen carrier (p. 352), such as iron or iodine, 
is present, action takes place readily at ordinary temperatures 
even in the dark, and substitution products are formed. 



CHAPTER XIX. 

CONSTITUTION OF BENZENE, AND ISOMERISM OF BENZENE 
DERIVATIVES. 

It will be seen from the facts just stated that although 
benzene, like the paraffins, is an extremely stable sub- 
stance, it differs from them very considerably in chemical 
behaviour, more especially in being comparatively readily 
acted on by nitric acid, sulphuric acid, and halogens, and 
in forming additive products with the last-named under 
certain conditions ; if, again, its properties be compared 
with those of the unsaturated hydrocarbons of the ethylene 
or acetylene series, the contrast is even more striking, par- 
ticularly when it is borne in mind that the proportion of 
carbon to hydrogen in the molecular formula of benzene, 



314 CONSTITUTION OF BENZENE, 

C 6 H 6 , would seem to indicate n relation to these unsaturated 
hydrocarbons. 

In order, then, to obtain some clue to the constitution of 
benzene, it is clearly of importance to carefully consider 
the properties of other mi saturated hydrocarbons of known 
constitution, and to ascertain in what respects they differ 
from benzene ; for this purpose the compound dipfopargyt, 
CH!C.CH 2 .GH 2 -C;CH (Part I. p. 87), may be chosen, as 
it has the same molecular formula as benzene. 

Now, although dipropargyl and benzene are isomeric, they 
are absolutely different in chemical behaviour; the former 
is very unstable, readily undergoes polymerisation, combines 
energetically with bromine, giving additive compounds, and 
is immediately oxidised even by weak agents ; it shows, 
in fact, all the properties of an unsaturated hydrocarbon of 
the acetylene series. Benzene, on the other hand, is ex- 
tremely stable, is comparatively slowly acted on by bromine, 
giving (usually) substitution products, and is oxidised only 
very slowly even by the most powerful agents. Since, 
therefore, dipropargyl must be represented by the above 
formula in order to account for its method of forma- 
tion and chemical properties, the constitution of benzene 
could not possibly be expressed by any similar formula, 
such as 

CHs-CiC-C-C-CHg or CH 2 :C:CH.CH:C:CH 2 , 

because compounds similar in constitution are always more 
or less similar in properties, and any such formula would 
not afford the slightest indication of the enormous differences 
between benzene and ordinary unsaturated hydrocarbons of 
the ethylene or acetylene series. 

These, and many other facts which were established during 
the investigation of benzene and its derivatives, led Kekule 
in 1865 to the conclusion that the six carbon atoms in benzene 
form a closed-chain or nucleus, that the molecule of benzene is 
symmetrical, and that each carbon atom is directly united with 



AND ISOMEU1SM OF BENZENE DERIVATIVES. 315 

one (and only one) atom of hydroyen, as may be represented 
by the formula, 




H c c H 



These views are now universally accepted, as the evidence 
which can be brought forward in support of them is most 
conclusive ; there is, however, at least one important point 
which has still to be settled before it can be said that the 
constitution of benzene is established as far as present theories 
permit. The point referred to is, the manner in which the 
carbon atoms are united with one another. The whole 
theory of the constitution of organic compounds is based 
on the assumption that carbon is always tetravalent, and 
this assumption, as already explained (Part I. p. 51), is 
expressed in graphic formulas by drawing four lines from 
each carbon atom, in such a way as to show what other 
atoms or groups the particular carbon atom in question is 
directly united with. Now, if this be done in the case of 
benzene, it is clear that two of the four lines or bonds, 
which represent the valencies of each carbon atom, must be 
drawn to meet two other carbon atoms, because unless each 
carbon atom is directly united with two others, the six could 
not together form a closed-chain; a third line or bond is 
easily accounted for, because each carbon atom is directly 
united with hydrogen. In this way, however, only three of 
the four affinities of each carbon atom are disposed of, and 
the next question, then, to be considered is, how may the 
fourth affinity or combining power of each carbon atom be 
represented so as to give the clearest indication of the 
behaviour of benzene*? Many chemists have attempted to 
answer this question, and several constitutional formulae for 



316 



CONSTITUTION OF BENZENE, 



benzene Lave been put forward ; that suggested by Kekule* 
in 1865, and given below, was for a long time considered 
to be the most satisfactory, but others, such as those of 
Glaus and Ladenburg, have also received support. 



H-C 



H G 




C H 



H 



C H H-C 




C H H 



C II H 



C 

i 

Clans. 
(Diagonal formula.) 




C-H 



C-H 



Ladenburg. 
(Prism formula.) 



It will be seen that these three formulae all represent the 
molecule of benzene as a symmetrical closed-chain of six 
carbon atoms, and that they differ, in fact, only as regards 
the way in which the carbon atoms are represented as being 
united with one another; a little consideration will make 
it clear, moreover, that the only difference between them 
lies in the manner of indicating the state or condition of the 
fourth affinity of each carbon atom. In Kekule's formula, 
for example, two lines (or a double bond) are drawn between 
alternate carbon atoms, a method of representation which is 
analogous to that adopted in the case of ethylene and other 
olefmes; in the formulae of Glaus and Ladenburg, on the 
other hand, each carbon atom is represented as directly 
united with three others (but with a different three in the 
two cases). 

As it would be impossible to enter here into a discussion 
of the relative merits of the above three formulae, it may 
at once be stated that they are all to some extent unsatis- 
factory, as they do not account for -certain facts which have 
been established by Baeyer and others during an extended 
study of benzene derivatives. In order to meet these 
objections, it was suggested by Armstrong, and shortly 



AND ISOMERISM OP BENZENE DERIVATIVES. 317 

afterwards by Baeyer, that the constitution of benzene 
should be represented by the formula, 




A 

Armstrong, Baeyer (Centric formula). 

which, although in the main similar to those given above, 
especially to that of Glaus, differs from them all in this : 
The fourth affinity of each of the six carbon atoms is repre- 
sented as merely directed towards a centre (as shown by 
the short lines) in order to indicate that, by the mutual 
action of the six affinities, the power of each is rendered 
latent, without bringing about actual union with another 
carbon atom. This formula, named by Baeyer the centric 
formula, summarises all facts relating to benzene and its 
derivatives, at least as well as, and in some respects better 
than, any which has yet been advanced ; unlike Kekule's 
formula, it does not represent benzene as containing ' double 
bindings ' similar to those in the olefines, and thus it affords 
some indication of the great difference between benzene 
and the olefines in chemical behaviour ; the very indefinite- 
ness of the centric formula may, in fact, be regarded as 
a point in its favour until more is known of the nature 
of chemical affinity, and it is, therefore, generally adopted 
at the present time. 

It now becomes necessary to give at greater length a 
few of the more important arguments which, in addition to 
those already considered, have led to the conclusion that 
the molecule of benzene consists of a symmetrical closed- 
chain of six carbon atoms, each of which is united with 
one atom of hydrogen ; also to point out how simply and 
accurately this view of its constitution accounts for a number 



318 CONSTITUTION OF BENZENE, 

of facts, relating to benzene and its derivatives, which would 
otherwise be incapable of explanation. 

In the first place, then, it may be repeated that benzene 
is a very stable substance ; although it is readily acted on 
by powerful chemical agents, such as nitric acid, sulphuric 
acid, and bromine, and thereby converted into new com- 
pounds, all these products or derivatives of benzene contain 
six carbon atoms ; the hydrogen atoms may be displaced 
by certain atoms or groups, which, in their turn, may be 
displaced by others, but in spite of all these changes, the 
six atoms of carbon remain, forming, as it were, a stable 
and permanent nucleus. This is expressed in the formula 
by the closed-chain of six carbon atoms, all of which are 
represented in the same state of combination, which implies 
that there is no reason why one should be attacked and 
taken away more readily than another. 

Again, a great many compounds, which are known to 
be derivatives of benzene, contain more than six atoms of 
carbon; when, however, such compounds are treated in a 
suitable manner, they are easily converted into substances 
containing six, but not less than six, atoms of carbon. This 
fact shows that in these benzene derivatives there are six 
atoms of carbon which are in some way different from the 
others, and this is also accounted for by assuming the 
existence of the stable nucleus ; the additional carbon atoms, 
not forming part of, but being simply united with, this 
nucleus, are more easily attacked and removed. 

Further, it must be remembered that although benzene 
usually gives substitution products, it is capable, under 
certain conditions, of forming additive products of the type 
C 6 H 6 X 6 ; this behaviour is also accounted for, since, in the 
formula, only three of the four affinities of each carbon atom 
are represented as actively engaged, and each carbon atom is 
therefore capable of combining directly with one monovalent 
atom or group, so as to form finally a fully saturated com- 
pound of the type, 



AND ISOMEKISM OF BENZENE DERIVATIVES. 319 




Isomerism of Benzene Derivatives. 

The most convincing evidence that the molecule of benzene 
is symmetrical is derived from a study of the isomerism of 
benzene derivatives. It has been proved, in the first place, 
that it is possible to substitute 1, 2, 3, 4, 5, or 6 monovalent 
atoms or groups for a corresponding number of the hydrogen 
atoms in benzene, compounds such as bromobenzene, C 6 H 5 Br, 
dinitrobenzene, C 6 H 4 (N0 2 ) 2 , trimethylbenzene, C 6 H 3 (CH 3 ) 3 , 
tetrachlorobenzene, C 6 H 2 C1 4 , pentamethylbenzene, C 6 H(CH 3 ) 5 , 
and hexacarboxybenzene, C 6 (COOH) 6 , being produced; the 
substituting atoms or groups may, moreover, be identical or 
dissimilar. 

An examination of such substitution products of benzene 
has shown that when only one, atom of hydrogen is displaced 
by any given atom or group, the same compound is always 
produced that is to say, the mono-substitution products of 
benzene exist only in one form ; when, for example, one atom 
of hydrogen is displaced by a nitro-group, no matter in what 
way this change may be brought about, the same substance, 
nitrobenzene, C 6 H 5 -N0 2 , is always produced. 

This might be explained, of course, by assuming that 
one particular hydrogen atom was always displaced first; 
when, for example, acetic acid is treated with soda, only 
one of the four hydrogen atoms is displaceable, and con- 
sequently the same salt is invariably produced. In the case 
of benzene, however, it has been shown that the same sub- 
stance is formed no matter which of the six hydrogen atoms 
is displaced. 



320 CONSTITUTION OP BENZENE, 

The only possible conclusion to be drawn from this fact 
is, that all the hydrogen atoms are in exactly similar posi- 
tions relatively to the rest of the molecule ; if this were not 
so, and the constitution of benzene were represented by a 
formula, such as the following, 

(a) H-C 

ll 

(a) H <y | \C-H (a) 
H H 



in which the hydrogen atoms are not all identically situated, 
it would be possible, by displacing one of them, to obtain 
(at least) two isomeric products; one by displacing one of 
the (a), another by displacing one of the (&), hydrogen atoms. 

As an example of the way in which it has been proved that 
the six hydrogen atoms in benzene are all similarly situated, the 
following may serve (Ladenburg) : Phenol, C 6 H 5 -OH, or hydroxy- 
benzene, obtained indirectly by displacing one atom of hydrogen 
(A) by the hydroxyl-group, may, with the aid of phosphorus 
pentabromide, be directly converted into bromobenzene, C 6 H 5 Br, 
and the latter may be transformed into benzoic acid (or carboxy- 
benzene), C 6 H 5 -COOH (A), by submitting it to the action of 
sodium and carbon dioxide ; as tliese three substances are pro- 
duced from one another by simple interactions, there is every 
reason to suppose that the carboxyl -group in benzoic acid is 
united with the same carbon atom as the bromine atom in bromo- 
benzene and the hydroxyl-group in phenol ; that is to say, that 
the same hydrogen atom (A) has been displaced in all three cases. 
Now three different hydroxybenzoic acids of the composition 
C 6 H 4 (OH)-COOH are known, and these three compounds may be 
either converted into or obtained from benzoic acid, C 6 H 5 -COOH 
(A), the difference between them being due to the fact that the 
hydroxyl-group has displaced a different hydrogen atom (B.C.D.) 
in each case ; each of these hydroxybenzoic acids forms a calcium 
salt which yields phenol on distillation (the carboxyl-group being 
displaced by hydrogen), and the three specimens of phenol thus 
produced are identical with the original phenol ; it is evident, 
therefore, that at least four (A.B.C.D.) hydrogen atoms in benzene 
are in the same state of combination, and occupy the same relative 



AND ISOMERISM OF BENZENE DERIVATIVES. 321 

position in the molecule ; in a somewhat similar manner it can be 
shown that this is true of all six. 

By substituting two monovalent atoms or groups for two 
of the atoms of hydrogen in benzene, three, but not more 
than three, substances having different properties are obtained ; 
there are, for example, three dinitrobenzenes, C 6 H 4 (N0 2 ) 2 , 
three dibromobenzenes, C 6 H 4 Br 2 , three dihydroxybenzenes, 
C 6 H 4 (OH) 2 , three nitrohydroxy benzenes, C 6 H 4 (N0 2 )-OH ; and 
so on. 

Now the existence of these three isomerides can be 
accounted for in a very simple manner with the aid of the 
formula already given, which, for this purpose, may con- 
veniently be represented by a simple hexagon, numbered as 
shown, the symbols C and H being omitted for the sake of 
simplicity. 




Suppose that any mono-substitution product, C 6 H 5 X, which, 
as already stated, exists only in one form, be converted into a 
di-substitution product, C 6 H 4 X 2 ; then if it be assumed that 
the atom or group (X) first introduced occupied any given 
position, say that numbered 1, the second atom or group may 
have substituted any one of the hydrogen atoms at 2, 3, 4, 5, 
or 6, giving a substance the constitution of which might be 
represented by one of the following five formulas : 



[ 1 [ 1 : 

-x 



I. II. III. IV. V. 

These five formulae, however, represent three isomeric sub- 
stances, and three only. The formula iv. represents .a 

Org. Chem. U 






322 CONSTITUTION OF BENZENE, 

compound in which the several atoms occupy the same 
relative positions as in the substance represented by the 
formula n., and for the same reason the formula v. is 
identical with. I. Although there is at first sight an 
apparent difference, a little consideration will show that 
this is simply due to the fact that the formulae are viewed 
from one point only; if the formulae IV. and v. be written 
on thin paper and then viewed through the paper, it will 
be seen at once that they are identical with n. and I. 
respectively. Each of the formulae i., n., and in., on the 
other hand, represents a different substance, because in no 
two cases are all the atoms in the same relative positions ; 
in other words, the di-substitution products of benzene exist 
theoretically in three isomeric forms. 

In the foregoing examples the two substituting atoms or 
groups have been considered to be identical, but even when 
they are different, experience has shown that only three 
di-substitution products can be obtained, and this fact, again, 
is iji accordance with the theory. If in the above five 
formulas a Y be written in the place of one X to express a 
difference in the substituting groups, it will be seen that, 
as before, the formula i. is identical with v., and n. with iv., 
but that i., ii., and in. all represent different arrangements 
of the atoms that is to say, three different substances. 

Since the di-substitution products of benzene exist in three 
isomeric forms, it is convenient to have some way of dis- 
tinguishing them by name ; for this reason all di-substitution 
products which are found to have the constitution repre- 
sented by formula i. are called ortho-compounds, and the 
substituting atoms or groups are said to be in the ortho- or 
1 : 2-position to one another ; those substances which may be 
represented by the formula 11. are termed meta-compounds, 
and the substituting atoms or groups are spoken of as occupy- 
ing the meta- or 1 : 3-position ; the term para is applied to 
compounds represented by the formula IIL, in which the atoms 
or groups are situated in the para- or l:4-position. 



AND ISOMER1SM OF BENZENE DERIVATIVES. 323 

Ortho-compounds, then, are those in which it is assumed, 
for reasons given below, that the two substituting atoms or 
groups are combined with carbon atoms which are themselves 
directly united; instead of expressing the constitution of 
any ortho-compound by the formula I., and representing the 
substituting atoms or groups as combined with the carbon 
atoms 1 and 2, it would therefore be just the same if they 
were represented as united with the carbon atoms 2 and 3, 
3 and 4, 4 and 5, 5 and 6, or 6 and 1 ; the arrangement 
of all the atoms would be the same, because the benzene 
molecule is symmetrical, and the numbering of the carbon 
atoms simply a matter of convenience. In a similar manner 
the substituting atoms or groups in meta-compounds may be 
represented as combined with any two carbon atoms which 
are themselves not directly united, but linked together by 
one carbon atom j it is quite immaterial which two carbon 
atoms are chosen, since atoms or groups occupying the 1:3, 
2:4, 3:5, 4:6, or 5:l-position are identically situated with 
regard to all the other atoms of the molecule. For the same 
reason para-compounds may be represented by placing the sub- 
stituting atoms or groups in the 1:4, 2:5, or 3:6-position. 

When more than two atoms of hydrogen in benzene are 
substituted, it has been found that the number of isomerides 
differs according as the substituting atoms or groups are 
identical or not. By displacing three atoms of hydrogen 
by three identical atoms or groups, three isomerides can be 
obtained, three trimethylbenzenes, C 6 H 3 (CH 3 ) 3 , for example, 
being known. Again, the existence of these isomerides can 
be easily accounted for, since their constitutions may be 
represented as follows, 



-x 
-x 

1:2:3- or Adjacent. 1:2:4- or Asymmetrical. 1:3:5- or Symmetrical. 








324 CONSTITUTION OP BENZENE, 

No matter in what other positions the substituting atoms or 
groups be placed, it will be found that the arrangement is 
the same as that represented by one of the formulae (p. 323) ; 
the position 1:2:3, for example, is identical with 2:3:4, 3:4:5, 
&c. ; 1:3:4 with 2:4:5, 3:5:6, &c.; and 1:3:5 with 2:4:6. For 
the purpose of referring to such tri-substitution products, the 
terms already given are often employed. 

The tetra-substitution products of benzene, in which all 
the substituting atoms or groups are identical, also exist in 
three isomeric forms represented by the following formulae, 



x- 



1:2:3:4. 1:2:3:5. 

When, however, five or six atoms of hydrogen are displaced 
by identical atoms or groups, only one substance is produced. 

When more than two atoms of hydrogen are displaced by atoms 
or groups which are not all identical, the number of isornerides 
which can be obtained is very considerable ; in the case of any tri- 
substitution product, C 6 H 3 X 2 Y, for example, six isomerides might 
be formed, as may be easily seen by assigning a definite position, 
say 1, to Y ; the isomerides would then be represented by formulae 
in which the groups occupied the position 1:2:3, 1:2:4, 1:2:5, 1:2:6, 
1:3:4, or 1:3:5, all of which would be different. In a similar 
manner the number of isomerides theoretically obtainable in the 
case of all benzene derivatives, however complex, may be deduced 
with the aid of the hexagon formula. 

All the cases of isomerism considered up to the present 
have been those due to the substituting atoms or groups 
occupying different relative positions in the benzene nucleus ; 
as, however, many benzene derivatives contain groups of atoms 
which themselves exist in isomeric forms, such compounds 
also exhibit isomerism exactly similar to that already met 
with in the case of the paraffins, alcohols, &c. There are, 
for example, two isomeric hydrocarbons of the composition 



AND ISOMERISM OF BENZENE DERIVATIVES. 325 

C 6 H 5 -C 3 H 7 , namely, propyl benzene, C 6 H 5 -CH 2 -CH 2 -CH 3 , and 
iaopropylbenzene, C 6 H 5 -CH(CH 3 ) 2 , just as there are two 
isomeric ethereal salts of the composition C 3 H 7 L As, 
moreover, propyl- and isopropyl-benzene, C 6 H 5 -C 3 H 7 , are 
isomeric with the three (ortho-, meta-, and para-) ethylmethyl- 
benzenes, C 6 H 4 (C 2 H 5 )-CH 3 , and also with the three (ad- 
jacent, symmetrical, and asymmetrical) trimethylbenzenes, 
C 6 H 3 (CH 3 ) 3 , there are in all eight hydrocarbons of the 
molecular formula, C 9 H 12 , derived from benzene. 

In studying the isomerism of benzene derivatives, the 
clearest impressions will be gained by invariably making use 
of a simple, unnumbered hexagon to represent C 6 H 6 , and by 
expressing the constitutions of simple substitution products 
by formulae such as, 
ci OH 

- H ! ! I I 

~CH 3 



Chlorobenzene. Pyrocatechol. Nitroplienol. Trimetliylbenzene. 

The omission of the symbols C and H is attended by no 
disadvantage whatsoever, because, in order to convert the 
above into the ordinary molecular formulae, it is only necessary 
to write C 6 instead of the hexagon, and then to count the 
unoccupied corners of the hexagon to find the number of 
hydrogen atoms in the nucleus, the substituting atoms or 
groups being added afterwards. In the case of chlorobenzene, 
for example, there are five unoccupied corners, so that the 
molecular formula is C 6 H 5 C1 ; whereas in the case of tri- 
methylbenzene there are three, and the formula, therefore, is 
C 6 H 3 (CH 3 ) 3 . 

As, however, such graphic formulae occupy a great deal of 
space, their constant use in a text-book is inconvenient, and 
other methods are adopted. The most usual course in the 
case of the di-derivatives is to employ the terms ortho-, meta-, 






326 CONSTITUTION OP BENZENE, 

and para-, or simply the letters o, m, and p, as, for example, 
ortho-dinitrobenzene or o-dinitrobenzene, nieta-nitraniline or 
m-nitraniline, para-nitrophenol or j9-nitrophenol ; the relative 
positions of the atoms or groups may also be expressed by 
numbers ; o-chloronitrobenzene, for example, may be described 

Cl (i) l 2 

as l:2-chloronitrobenzene, as C 6 H 4 <,,,.~ , or as C 6 H 4 C1-N0 2 , 

the corresponding para-compound as l:4-chloronitrobenzene, 
as C 6 B^<9^ (1) , or as C 6 H 4 C1-N0 2 . In the case of the tri- 



derivatives the terms symmetrical, asymmetrical, and adjacent 
(compare p. 323) may be employed when all the atoms or 
groups are the same, but when they are different the constitu- 
tion of the compound is usually expressed with the aid of 
Miimbers ; the tribromaniline of the constitution, 




Br 



1 246 

for example, is described as C 6 H 2 Br 3 'NH 2 [NH 2 :Br:Br:Br], or 
as C 6 H 2 Br 3 -NH 2 [NH 2 :3Br = 1:2:4:6], but it is of course quite 
immaterial from which corner of the imaginary hexagon the 
numbering is commenced. 

Determination of the Constitution of Benzene Derivatives. 

It has been pointed out that the di-substitution products of 
benzene, such as dibromobenzene, C 6 H 4 Br 2 ; dihydroxybenzene, 
C 6 H 4 (OH) 2 ; and nitraniline, C 6 H 4 (N0 2 )-NH 2 , exist in three 
isomeric forms, and that their isomerism is due to the different 
relative positions of the substituting atoms or groups in the 
benzene nucleus ; it is evident, however, that in order to arrive 
at the constitution of any one of these substances, and to be 
able to say whether it is an ortho-, meta-, or para-compound, 
a great deal of additional information is required. 



AND ISOMERISM OP BENZENE DERIVATIVES. 327 

Now the methods which are adopted in deciding questions 
of this kind at the present time are comparatively simple, but 
they are based on the results of work which has extended 
over many years. One of the most important results of such 
work has been to prove that a given di-substitution product 
of benzene may be converted by more or less direct methods 
into many of the other di-substitution products of the same 
series; or^o-dinitrobenzene, C 6 H 4 (N0 2 ) 2 , for example, may 
be transformed into o-diamidobenzene, C 6 H 4 (NH 2 ) 2 ; o-dihy- 
droxybenzene, C 6 H 4 (OH) 2 ; o-dibromobenzene, C 6 H 4 Br 2 ; o-di- 
methylbenzene, C 6 H 4 (CH S ) 2 , and so on, corresponding changes 
being also possible in the case of meta- and para-compounds. 
If, therefore, it can be ascertained to which series a given 
di-substitution product belongs, the constitution of other 
di-substitution products which may be derived from, or 
converted into it, is thereby determined. There are, for 
example, three dinitrobenzenes melting at 90, 116, and 173 
respectively ; now if it could be proved that the compound 
melting at 90 is a meta-derivative, then it would necessarily 
follow that the diamido-, dihydroxy-, dibromo-, and other di- 
derivatives of benzene obtained from this particular dinitro- 
compound by substituting other atoms or groups for the two 
nitro-groups, must also be meta-compounds ; it would also be 
known that the di-derivatives of benzene obtained from the 
other two dinitrobenzenes, melting at 116 and 173 respec- 
tively, in a similar manner must be either ortho- or para- 
compounds respectively. 

Obviously, then, it is necessary, in the first place, to 
determine the constitution of those di-derivatives which are 
afterwards to be used as standards. 

As an illustration of the methods and arguments originally 
employed in the solution of problems of this nature, the case 
of the dicarboxy- and dimethyl-derivatives of benzene may 
be quoted. Of the three dicarboxybenzenes, C 6 H 4 (COOH) 2 , 
one namely, phthalic acid (p. 438) is very readily converted 
into its anhydride, but all attempts to prepare the anhydrides 



328 



CONSTITUTION OF BENZENE, 



of the other two acids (isophthalic acid and terephthalic 
acid, pp. 439, 440) result in failure ; it is assumed, therefore, 
that the acid which gives the anhydride is the o-compound, 
because, from a study of the behaviour of many other dicarb- 
oxylic acids, it has been found that anhydride formation 
takes place most readily when the two carboxyl-groups are 
severally combined with two carbon atoms which are them- 
selves directly united, as, for example, in the case of succinic 
acid. In other words, if the graphic formulae of succinic 
acid and of the three dicarboxy-derivatives of benzene be 
compared, it will be evident that in the o-compound the 
relative position or state of combination of the two carboxyl- 
groups is practically the same as in succinic acid, but quite 
otherwise in the case of the m- and ^-compounds. 

COOH 

For this, and other reasons not stated here, phthalic acid 
may be provisionally regarded as an ortf/io-dicarboxybenzene. 

Again, the hydrocarbon mesitylene or trimethylbenzene, 
C 6 H 3 (CH 3 ) 3 , may be produced synthetically from acetone 
(p. 348), and its formation in this way can be explained in 
a simple manner only by assuming that mesitylene is a 
symmetrical trimethylbenzene of the constitution (A), 



Ul 

L 



CH 2 -cooH X^^\_coo: 
I J coo 



2-COOH 



COOH S ^v COOH 
COOH I I 



CH* 



CH 3 - 




-CH 3 



CH 



-CH 3 



COOH 




-CH 3 



COOH 
Mesitylenic Acid. 



-COOH 



Dimetliylbenzene. 
(m-Xylene.) 



Isophthalic Acid. 



AND ISOMERISM OF BENZENE DERIVATIVES. 329 

When this hydrocarbon is carefully oxidised, it yields an acid 
(B) of the composition C 6 H 3 (CH 3 ) 2 -COOH (by the conver- 
sion of one of the methyl-groups into carboxyl), from which 
a dimethylbenzene, C 6 H 4 (CH 3 ) 2 (C), is easily obtained by 
the substitution of hydrogen for the carboxyl-group. This 
dimethylbenzene, therefore, is a meta-com pound, because no 
matter which of the original three methyl-groups in mesityl- 
ene has been finally displaced by hydrogen, the remaining 
two must occupy the m-position. Now when this dimethyl- 
benzene is oxidised with chromic acid, it is converted into a 
dicarboxylicacid (D) namely, isophthalic acid, C 6 H 4 (COOH) 2 , 
which, therefore, must also be regarded as a meta-compound ; 
the constitution of two of the three isomeric dicarboxy-deriva- 
tives of benzene having been thus determined, the third 
namely, terephthalic acid, can only be the j>ara-com pound. 

It is now a comparatively simple matter to ascertain to 
which series any of the three dimethylbenzenes belongs; 
one of them having been found to be the meta-compound, 
all that is necessary is to submit each of the other two to 
oxidation, and that which gives phthalic acid will be the 
ortho-compound, whilst that which yields terephthalic acid 
will be the para-derivative. Moreover, the constitution of 
any other di-substitution product of benzene may now be 
determined without difficulty, provided that it is possible 
to convert it into one of these standards by simple reactions. 

As the methods which have just been indicated are based 
entirely on arguments drawn from analogy, or from deductions 
as to the probable course of certain reactions, the conclusions 
to which they lead cannot be accepted without reserve ; there 
are, however, several other ways in which it is possible to 
distinguish with much greater certainty between ortho-, meta-, 
and para-compounds, and of these that employed by Kb'rner 
may be given as an example. 

Kbrner's method is based on the fact that, if any di- 
substitution product of benzene be converted into a tri- 
derivative by further displacement of hydrogen of the 



330 



CONSTITUTION OF BENZENE, 



nucleus, the number of isomerides which may be obtained 
from an ortho-, raeta-, or para-compound is different in 
the three cases, so that by ascertaining the number of 
these products the constitution of the original di-derivative 
may be established. In the investigation of the dibromo- 
benzenes, C 6 H 4 Br 2 , for example, three isomerides melting 
at - 1, +1, and 89 respectively were discovered, and 
the question arose, which of these is the ortho-, which the 
meta-, and which the para-compound 1 ? Suppose now that 
each of these isomerides is separately converted into a tri- 
bromobenzene of the composition C 6 H 3 Br 2 -Br ; then, if it be 
the or^/w-dibromo-compound, it is possible to obtain from it 
two, but only two, tribromobenzenes, because, although there 
are four hydrogen atoms, any one of which may be displaced, 




-Br 



-Br 




-Br 



Br- 




Br Br- 




Br 



III. 



IV. 



the compound of the constitution in. is identical with IL, 
and iv. with i., the relative positions of all the atoms being 
the same in the two cases respectively. 

If, on the other hand, the dibromobenzene be the meta- 
compound, it might yield three, but only three, isomeric 
tri-derivatives, which would be represented by the first 
three of the following formulae, the fourth being identical 
with the second, 




Br 



-Br 




Br Br- 




Br- 



Br 




-Br 



Finally, if the substance in question be 







AND ISOMERISM OP BENZENE DERIVATIVES. 331 

benzene, it could give only one tri-derivative, the following 
four formulae being identical, 



-Br ^ >i fT- >^ Br- 

-Br Br 



Experiments showed that the compound melting at 1 
gave two tribromobenzenes ; it is therefore the ortho-com- 
pound.. The dibromobenzene melting at +1 gave three 
such derivatives, and is thus proved to be the meto-compound ; 
the isomeride melting at 89 gave only one, and -is therefore 
the jmra-compound. It is obvious, then, that this method 
may be applied in ascertaining to which series any di- 
substitution product belongs; it may also be employed in 
determining the constitution of the tri-derivatives in a 
similar manner. 

At the present time the constitution of any new benzene 
derivative is, as a rule, very easily ascertained, because it 
is simply converted into one of the many compounds of 
known constitution. 



CHAPTER XX. 

GENERAL PROPERTIES OF AROMATIC COMPOUNDS. 

Classification of Organic Compounds. The examples 
given in the foregoing pages will have afforded some in- 
dication of the large number of compounds which it is 
possible to prepare from benzene, by the substitution of 
various elements or groups for atoms of hydrogen; as the 
substances formed in this way, and many other benzene 
derivatives which occur in nature, or may be prepared 
synthetically, still retain much of the characteristic chemical 



332 GENERAL PROPERTIES OF AROMATIC COMPOUNDS. 

behaviour of benzene, and differ in many respects from 
the paraffins, alcohols, acids, and all other compounds pre- 
viously considered (Part I.), it is convenient to class benzene 
and its derivatives as a separate group. 

Organic compounds are therefore classed in two principal 
divisions, the fatty or aliphatic (from #Xei0a/>, fat) and the 
aromatic. The word 'fatty,' originally applied to some of 
the acids of the C n H 2n 2 series (Part I. p. 145), is now used 
to denote all compounds which may be considered as deriva- 
tives of marsh-gas, and which cannot be regarded as directly 
derived from benzene ; all the compounds described in Part I. 
belong to the fatty group or division. Benzene and its 
derivatives, on the other hand, are classed in the ' aromatic ' 
group, this term having been first applied to certain naturally 
occurring compounds (which have since been proved to be 
benzene derivatives) on account of their peculiar aromatic 
odour. 

The fundamental distinction between fatty and aromatic 
compounds is one of constitution. All derivatives of benzene, 
and all other compounds which contain a closed-chain or nucleus 
similar to that of benzene, are classed as aromatic. Fatty 
compounds, on the other hand, such as CH 3 -CH 2 -CH 2 -CH 3 , 
CH 2 (OH).CH(OH).CH 2 (OH), and COOILCH 2 .CH 2 .COOH, 
do not, as a rule, contain a closed-, but an open-chain* of 
carbon atoms ; such compounds, moreover, may be regarded 
as derived from marsh-gas by a series of simple steps. 

It must not be supposed, however, that all aromatic com- 
pounds are sharply distinguished from all aliphatic or fatty 
substances, or that either class can be defined in very exact 
terms. The mere fact that the constitution of a substance 
must be represented by a closed-chain formula does not 
make it an aromatic compound ; succinimide (Part I. p. 243), 

* The terms 'open-chain' and 'closed-chain' originated in the chain-like 
appearance of the graphic formulae as usually written, and are not intended 
to convey the idea that the atoms are joined together by any form of 
matter, or that they are all arranged in straight lines. 



GENERAL PROPERTIES OF AROMATIC COMPOUNDS. 333 

for example, although it is a closed-chain compound, is clearly 
a member of the fatty series, because of its relationship to 
succinic acid. Although, again, the members of the aromatic 
group may all be regarded as derivatives of benzene, they 
may also be considered as derived from marsh-gas, since 
not only benzene itself, but many other aromatic compounds, 
may be directly obtained from members of the fatty series 
by simple reactions, arid, conversely, many aromatic com- 
pounds may be converted into those of the fatty series. 

Some examples of the production of aromatic from fatty 
compounds have already been given namely, the formation 
of benzene by the polymerisation of acetylene, and that 
of mesitylene by the condensation of acetone ; these two 
changes may be expressed graphically in the following 

manner, 

H 

CH 
^ 

C H 

U ' 



, 

H; 



CH 3 CH 3 

CO C 

CH 3 

CO-C 



CH 3 -CO CO-CH 3 



and may be regarded as typical reactions, because many other 
substances, similar in constitution to acetylene and acetone 
respectively, may be caused to undergo analogous trans- 
formations. Bromacetylene, CBriCH, for example, may be 
converted into (symmetrical) tribromobenzene, simply by 
leaving it exposed to direct sunlight, 



and methylethyl ketone (a homologue of acetone) is trans- 
formed into symmetrical triethylbenzene (a homologue of 



334 GENERAL PROPERTIES OF AROMATIC COMPOUNDS. 

mesitylene or trimethylbenzene) by distilling it with sulph- 
uric acid, 

3CH 3 .CO.C 2 H 5 = C 6 H 3 (C 2 H 5 ) 3 + 3H 2 0. 

General Character of Aromatic Compounds. Although, 
then, it is impossible to draw any sharp line between fatty 
and aromatic compounds, and many substances are known 
which form a connecting link between the two classes, the 
great majority of aromatic substances differ materially from 
those of the fatty division in constitution, and consequently 
also in properties. 

Speaking generally, aromatic compounds contain a larger 
percentage of carbon and have a higher molecular weight 
than those of the fatty division, and for these reasons 
they are more frequently crystalline at ordinary temperatures. 
They are, as a rule, less readily resolved into simple sub- 
stances than are the members of the fatty series (except 
the very stable paraffins), although in most cases they are 
more easily converted into substitution products. Their 
behaviour with nitric acid and with sulphuric acid is very 
characteristic, and distinguishes them from nearly all fatty 
compounds, inasmuch as they are, as a rule, readily con- 
verted into nitro- and sulphonic-derivatives respectively by 
the displacement of hydrogen atoms of the nucleus, 



C 6 H 5 .COOH + HN0 3 = C 6 H 4 < + H 2 



C 6 H 5 -OH + 3HN0 3 = C 6 H 2 (OH)(N0 2 ) 3 + 3H 2 



Fatty compounds rarely give sulphonic- or nitro-derivatives 
under the same conditions, but are oxidised and resolved 
into two or more simpler substances. 

When aromatic nitre-compounds are reduced, they are 
converted into amido-compounds, 

C fl H 6 .N0 2 + 6H = C 6 H 5 .NH + 2H 2 
C 6 H 4 (N0 2 ) 2 + 12H = C 6 H 4 (NH 3 ) 2 + 4H 2 0. 



GENERAL PROPERTIES OF AROMATIC COMPOUNDS. 335 

These amido-compounds differ from the fatty amines in 
at least one very important respect, inasmuch as they are 
converted into diazo-com pounds (p. 381) on treatment with- 
nitrous acid in the cold ; this behaviour is highly char- 
acteristic, and the diazo-compounds form one of the most 
interesting and important classes of aromatic substances. 

It has already been pointed out that benzene does not 
show the ordinary behaviour of unsaturated fatty compounds, 
although under certain conditions both the hydrocarbon and 
its derivatives are capable of forming additive compounds 
by direct combination with two, four, or six (but not with 
one, three, or five) monovalent atoms. This fact proves that 
benzene is not really a saturated compound like methane or 
ethane, for example, both of which are quite incapable of 
yielding derivatives except by substitution. Nevertheless, 
the conversion of benzene and its derivatives into additive 
products is, as a rule, much less readily accomplished than in 
the case of fatty, unsaturated compounds ; the halogen acids, 
for example, which unite directly with so many unsaturated 
fatty compounds, have no such action on benzene and its 
derivatives, and even in the case of the halogens and nascent 
hydrogen, direct combination occurs only under particular 
conditions. The additive compounds obtained from benzene 
and its derivatives form a connecting link between the 
members of the aromatic and fatty divisions. 

Benzene itself is reduced only with great difficulty, and when 
strongly heated with hydriodic acid it yields normal hexane, C 6 H 14 , 
as principal product, the closed-chain suffering disruption. 

Hexahydrobenzene (hexamethykne*), C 6 H 12 , is formed, but 
only in small quantities, when benzene is reduced with hydriodic 
acid ; it occurs in Russian petroleum, from which it can be isolated 
by repeated fractional distillation. It melts at 4-7, boils at 81, 
and when treated with bromine it gives bromohexahydrobenzene or 
bromohexamethylene (b.p. 162), 

C 6 H 12 + Br 2 = CfjHj jBr + HBr ; 

* The name hexamethylene serves to recall the fact that the compound 
is composed of six methylene (-CH 2 -) groups. 



336 



GENERAL PROPERTIES OP AROMATIC COMPOUNDS. 



when this bromo-derivative is digested with alcoholic potash, it is 
converted into tetrahydrobenzene, just as ethyl bromide is converted 
into ethylene under similar conditions. 

Tetrahydrobenzene, C 6 H 10 , boils at 83-84, and combines 
directly with bromine at ordinary temperatures, yielding dibroino- 
hexahydrobenzene or dibrornohexamethylene, C 6 H 10 Br 2 . 

Dihydrobenzene, C 6 H 8 , is obtained by heating dibromohexa- 
hydrobenzene with alcoholic potash or with quinoline (which acts 
like alcoholic potash and removes hydrogen bromide), 

C 6 H 10 Br 2 = C 6 H 8 + 2HBr ; 

it boils at 84-86, combines directly with bromine, giving a crystal- 
line tetrabromide, C 6 H 8 Br 4 , and rapidly oxidises on exposure to the 
air, being converted into a resin. 

The following formulae may serve to represent the above series of 
changes : 

CH CH 2 CHBr 

[<^T^>CH CH 2 X^ NCH 2 CH 2 ^\CH 2 

CHx' |^>|CH CH 2 ^^ ^JcH 3 CH 2 L^^ JcH 2 

CH CH 2 

Benzene. Hexahydrobenzene. 

(Hexainethylene.) 



CHi 



CH 2 

Bromohexahydrobenzene. 
(Broinohexamethylene.) 



CH 



CHBr 



CH 



CH 2 




CH 



CH 



CH 2 



CH 2 ^ ^^ CH 2 

CH 2 CH 2 

Tetrahydrobenzene. Dibromohexahydrobenzene. 

(Dibroinoliexaniethylene.) 




CHjj 1 ^ 1JOI1 
CH 2 

Dihydrobenzene. 



It is very important to note that dihydro- and tetrahydro- 
benzene, which must be regarded as incompletely or partially 
reduced benzene, differ very much from the original hydrocarbon, 
the difference being, in fact, much the same as that which exists 
between unsaturated and saturated compounds ; in other words, 
when benzene combines with two or four atoms of hydrogen, the 
product is no longer characterised by great stability, but shows the 
ordinary behaviour of unsaturated compounds, inasmuch as it is 
readily oxidised and readily combines with bromine ; this is also 
true in the case of all partially reduced benzene derivatives. 

As expressed by the above formulae, the conversion of benzene 
or of a benzene derivative into a di- or tetfra-additive product 



GENERAL PROPERTIES OF AROMATIC COMPOUNDS. 337 

is accompanied by a change in the mode of combination of all 
the carbon atoms ; two or four of the six carbon affinities (repre- 
sented in the centric formula by the short lines directed towards 
the centre) being required to take up the additive atoms, the 
remainder are released from their original state of combination, 
and become united in the same way as in ethylene. 

When the hydrogen atoms in benzene are displaced by 
groups or radicles which are composed of several atoms, 
these groups are spoken of as side-chains; ethylbenzene, 
C 6 H 5 .CH 2 .CH 3 , benzyl alcohol, C 6 H 5 -CH 2 .OH, and methyl- 
aniline, C 6 H 5 -NH-CH 3 , for example, would each be said to 
contain a side-chain, whereas the term would not, as a rule, 
be applied in the case of phenol, C 6 H 5 -OH, nitrobenzene, 
C 6 H 5 N0 2 , &c., where the substituting groups are compara- 
tively simple, and do not contain carbon atoms. 

Now the character of any particular atom or group in the 
side-chain, although influenced to some extent by the fact 
that the group is united with the benzene nucleus, is on the 
whole very similar to that which it possesses in fatty com- 
pounds. The consequence is that aromatic compounds con- 
taining side-chains of this kind have not only the properties 
already referred to, as characteristic of the derivatives of 
benzene, but show also, to a certain extent, the behaviour 
of fatty compounds. Benzyl chloride, C 6 H 5 -CH 2 C1, for ex- 
ample, may be directly converted into the nitro-derivative, 
C 6 H 4 (N0 2 ).CH 2 C1, and the sulphonic acid, C 6 H 4 (S0 3 H).CH 2 C1, 
reactions characteristic of aromatic compounds ; on the other 
hand, the -CH 2 C1 group may be transformed into -CH 2 -OH, 
-CHO, -COOH, and so on, just as may the same group in 
ethyl chloride, CH 3 -CH 2 C1, and similar fatty compounds, and 
in all cases the products retain, to some extent, the properties 
of fatty substances as long as the side-chain remains. The 
carbon atoms contained in the side-chains, however, are 
generally more easily attacked and separated from the rest of 
the molecule than are those of the closed-chain or nucleus ; 
when ethylbenzene. C 6 H 5 -CH 2 -CH 3 , or propylbenzene, 

Ortt. Chem, V 



338 



GENERAL PROPERTIES OF AROMATIC COMPOUNDS. 



C 6 H 5 -CH 2 -CH 2 -CH 3 , for example, is boiled with chromic acid, 
the side-chain undergoes oxidation, carbon dioxide is evolved, 
and benzoic acid, C 6 H 5 -COOH, is produced in both cases, the 
six atoms of carbon in the nucleus being unchanged (p. 429). 
Although the compounds derived from benzene by direct 
substitution are very numerous, the aromatic group also 
contains a great many other substances which are more 
distantly related to benzene, and which can only be re- 
garded as derived from it indirectly. The hydrocarbon 
dipTienyl, C 6 H 5 -C 6 H 5 , for example, which, theoretically, is 
formed by the union of two phenyl or C 6 H 5 - groups, just as 
dimethyl or ethane, CH 3 -CH 3 , is produced by the combina- 
tion of two methyl-groups, is an important member of the 
aromatic division, and, like benzene, is capable of yielding a 
very large number of substitution products. Other hydro- 
carbons are known in which the presence of two or more 
closed carbon chains, combined in different ways, must be 
assumed, as, for example, in the cases of naphthalene (p. 454) 
and anthracene (p. 470), 





Anthracene. 



Naphthalene. 

and there are also substances, such as pyridine (p. 485) and 
quinoline (p. 493), in which a nitrogen atom occupies the 
position of one of the CHfe groups in the closed-chain. 





Qninoline. 

All these, and many other compounds and their derivatives, 
are classed as aromatic, because they show the general be- 
haviour already referred to, and resemble benzene more or less 
closely in constitution. 



HOMOLOGOES OF BENZEXE, ETC. 339 

CHAPTER XXI. 

HOMOLOGUES OF BENZENE AND OTHER HYDROCARBONS. 

Benzene, the simplest hydrocarbon of the aromatic group, 
is also the first member of a homologous series of the general 
formula C w H 2n _ 6 ; the hydrocarbons of this series are derived 
from benzene by the substitution of alkyl-groups for hydrogen 
atoms, just as the homologous series of paraffins is derived 
from marsh-gas. The second member, toluene or methyl- 
benzene, C 6 H 5 -CH 3 , like benzene itself, exists in only one 
form, but the next higher homologue, which has the 
molecular composition C 8 H 10 , occurs in four isomeric forms 
namely, as ethylbenzene, C 6 H 5 -C 2 H 5 , and as ortho-, meta-, 
and para-dimethylbenzene, C 6 H 4 (CH 3 ) 2 ; on passing up the 
series, the number of theoretically possible isomerides rapidly 
increases. 

By substituting a methyl-group for one atom of hydrogen in 
the hydrocarbon C 8 H 10 , for example, eight isomerides of the com- 
position C 9 H 12 may theoretically be obtained, and are, in fact, 
known ; of these isomerides, five namely, propylbenzene and iso- 
propylbenzene, C 6 H 5 -C 3 H 7 , and o-, m- t and ja-methylethylbenzene, 
C 6 H 4 (CH 3 )-C 2 H 5 , are derived from ethylbenzene, the other three 
namely, symmetrical, adjacent, and asymmetrical trimethyl- 
benzene, C 6 H 3 (CH 3 ) 3 , being derived from the dimethylbenzenes. 

Most of the hydrocarbons of this series, and others which 
will be mentioned later, occur in coal-tar, from which they 
are extracted in much the same way as benzene; it is, 
however, exceedingly difficult to obtain any of them in a 
pure state directly from this source by fractional distillation, 
as the boiling-points of some of the compounds lie very close 
together; nevertheless, the process is now carried out on 
the large scale with such care and with such perfect apparatus 
that the purified compounds contain, in some cases, only traces 
of foreign substances. 



340 HOMOLOGUES OF BENZENE 

The homologues of benzene may be obtained by the 
following general methods : 

^(1) By treating benzene (or its homologues) with alkyl 
halogen compounds in presence of anhydrous aluminium 
chloride (Friedel and Crafts' reaction) ; under these condi- 
tions the hydrogen atoms of the nucleus are displaced by 
alkyl-groups, benzene and methyl chloride, for example, giving 
toluene, C 6 H 5 -CH 3 , xylene, C 6 H 4 (CH 3 ) 2 , trimethylbenzene, 
C 6 H 3 (CH 3 ) 3 , &c. ; whereas ethylbenzene, with the same alkyl 
compound, yields methylethylbenzene, C 6 H 4 (CH 3 )-C 2 H 5 ; di- 
methylethylbenzene, C ( .H 3 (CH 3 ) 2 -C 2 H 5 , and so on, 

C 6 H 6 + CH 3 C1 = C 6 H 5 .CH 3 + HC1 
C 6 H 6 + 2CH 3 C1 = C 6 H 4 (CH 3 ) 2 + 2HC1 
C 6 H 5 .C 2 H 5 + CH 3 C1 m C 6 H 4 (CH 3 ).C 2 H 5 + HC1. 

Anhydrous benzene, or one of its homologues, is placed in a flask 
connected with a reflux condenser, and about one-third of its weight 
of anhydrous aluminium chloride added ; the alkyl chloride or 
bromide is then passed into the liquid if a gas, or poured in if a 
liquid, arid the mixture heated on a water-bath until the evolution 
of hydrogen chloride or bromide is at an end ; the apparatus and 
materials must be dry. In some cases ether, carbon disulphide, or 
petroleum is previously mixed with the hydrocarbon in order to 
dilute it, experience having shown this to be advantageous. When 
quite cold, water is gradually added to dissolve the aluminium 
compounds, and after having been separated and dried with calcium 
chloride, the mixture of hydrocarbons is submitted to fractional 
distillation ; in some cases a preliminary distillation in steam is 
advisable. 

It is probable that an aluminium compound, such as C 6 H 5 .A1 2 C1 5 , 
is first formed with evolution of hydrogen chloride, this substance 
then interacting with the alkyl halogen compound to form the new 
hydrocarbon, aluminium chloride being regenerated, 

CH 8 . Al a Cl s + CH 3 C1 = C 6 H 5 -CH 3 + A1 2 C1 6 . 

Anhydrous ferric or zinc chloride may be employed in the place of 
aluminium chloride, but, as a rule, not so successfully. 

(2) By treating a mixture, consisting of a halogen deriva- 
tive of benzene or of one of its homologues, and an alkyl 



AND OTHER HYDROCARBONS. 341 

halogen compound, with sodium or potassium (Fittig's re- 
action) ; this method of formation is similar to that by which 
the higher paraffins may be synthetically produced from 
methane (Part I. p. 68), and has the advantage over Friedel 
and Crafts' method that the constitution of the product is 
known. Bromobenzene and methyl iodide, for example, give 
toluene, whereas o-, m-, or ;>-bromotoluene and ethyl iodide 
yield o-, m-, or ^-ethylmethylbenzene, 

C 6 H 6 Br + CH 3 I + 2Na - C 6 H 5 -CH 3 + Nal + NaBr 

pTT 

C 6 H 4 Br.CH 3 + C 2 H 5 I + 2K = C 6 H 4 < ^ + KBr + KI. 

^2^5 

The bromo - derivatives of the aromatic hydrocarbons are 
usually employed in such cases because the chloro-derivatives 
are not so readily acted on, and the iodo-compounds are not 
so easily prepared ; the alkyl iodides are also used in preference 
to the chlorides or bromides because they interact more readily. 
Dry ether is usually employed as a diluent. 

(3) By heating carboxy-derivatives of benzene and its 
homologues with soda-lime, a method analogous to that 
employed in converting the fatty acids into paraffins (Part I. 

P. 68); 

C 6 H 4 (CH 3 ).COOH = C 6 H 5 .CH 3 + C0 2 
C 6 H 4 (COOH) 2 - C 6 H 6 + 2C0 2 . 

(4) By passing the vapour of hydroxy-derivatives of 
benzene and its homologues over heated zinc-dust, which 
combines with the oxygen in the compound, 

C tt H 5 .OH + Zn - C 6 H 6 + ZnO 
C 6 H 4 (CH 3 ).OH + Zn = C 6 H 5 -CH 3 + ZnO. 

(5) By the destructive distillation of coal, wood, peat, &c., 
and by passing the vapour of many fatty compounds through 
red-hot tubes (compare p. 310). 

General Properties. Most of the homologues of benzene 
are colourless, mobile liquids ; one or two, however, are 
crystalline nt ordinary temperatures. They all distil with- 
out decomposing, are volatile in steam, and burn with 



342 HOMOLOGUES OF BENZENE 

a smoky flame ; they are insoluble in water, but miscible 
with (absolute) alcohol, ether, petroleum, &c., in all propor- 
tions; they dissolve fats and many other substances which 
are insoluble in water. 

Just as in other homologous series, the homologues of 
benzene show a gradual variation in physical properties with 
increasing molecular weight, but owing to the large number 
of isomerides, this is only obvious when corresponding com- 
pounds are compared ; as an example of this, the following 
?ttcw0-substitution products of benzene may be considered : 

Benzene, C 6 H 6 Sp. gr. at 0, 0-899 B.p., 80-5 

Toluene, C 7 H 8 0-882 110-3 

Ethylbenzene, C 8 H 10 0-883 .. 134 

Propylbenzene, C 9 H 12 n 0-881 .. 158 

There are, however, three hydrocarbons isomeric with 
ethylbenzene (p. 347), whilst propylbenzene has seven iso- 
merides (p. 339), so that the original homologous series 
given above branches into a number of series, in which the 
homology becomes rather confused. In the case of isomeric 
^'-substitution products there is usually some difference in 
physical properties, but the extent to which they differ is 
rather variable ; the three xylenes, C 6 H 4 (CH 3 ) 2 , for example, 
show the following differences : 

Orthoxylene. Metaxyleiie. Paraxylene. 

Sp. gr. at 0-893 0-881 880 

B.p. 142 139 138 (M.p. 15) 

As a general rule, to which, however, there are some ex- 
ceptions, para-compounds melt at a higher temperature than 
the corresponding meta-compounds, and the latter usually at 
a higher temperature than the corresponding ortho-compounds; 
the boiling-points also vary, but with less regularity. This 
applies to all benzene derivatives, not to hydrocarbons only. 

The homologues of benzene show the characteristic chemical 
behaviour of the simplest hydrocarbon, inasmuch as they 
readily yield nitro- and sulphonic-derivatives ; toluene, for 
example, gives nitrotoluene, C 6 H 4 (CH 3 )-N0 2 , and toluene- 



AND OTHER HYDROCARBONS, 343 

sulphonic acid, C (5 H 4 (CH 3 )-S0 3 H, xylene yielding nitro- 
xylene, C 6 H 3 (CH 3 ) 2 -N0 2 , and xylenesulphonic acid, 

' C 6 H 8 (CH 3 ) 2 .S0 8 H. 

In these, and in all similar reactions, the product invariably 
consists of a mixture of isomerides, the course of the reaction 
depending both on the nature of the interacting compounds 
and on the conditions of the experiment (compare p. 364) ; as 
a rule, the greater the number of alkyl-groups in the hydro- 
carbon, the more readily does it yield nitro- and sulphoiiic- 
derivatives. 

The fact that benzene and its liomologues gradually dissolve in 
concentrated sulphuric acid, especially on warming, is sometimes 
made use of in separating these aromatic hydrocarbons from 
the paraffins, as, for example, in the analysis of coal-gas ; their 
separation from unsaturated fatty hydrocarbons could not of 
course be accomplished in this way, as the latter are also dis- 
solved by concentrated sulphuric acid. 

All the homologues of benzene are very stable, and are with 
difficulty resolved into compounds containing a smaller number 
of carbon atoms ; powerful oxidising agents, however, such as 
chromic acid, potassium permanganate, and dilate nitric acid, 
act on them slowly, the alkyl-groups or side-chains being 
attacked, and as a rule converted into carboxyl-groups ; toluene 
and ethylbenzene, for example, give benzoic acid, whereas the 
xylenes yield dicarboxylic acids (p. 436), 

C 6 H 5 -CH 3 + 30 = C 6 H 5 -COOH + H 2 
C 6 H 5 .CH 2 .CH 3 + 60 = C 6 H 5 .COOH + C0 2 + 2H 2 
C 6 H 4 (CH 3 ) 2 + 60 = C 6 H 4 (COOH) a + 2H 2 0. 

Although in most cases oxidation leads to the formation of a 
carboxy-derivative of benzene, the stable nucleus of six carbon 
atoms remaining unchanged, some of the homologues are com- 
pletely oxidised to carbon dioxide and water (compare p. 347), 
and benzene itself undergoes a similar change on prolonged and 
vigorous treatment. 

Aromatic hydrocarbons, like those of the fatty series, may 
be regarded as hydrides of; hypothetical radicles ; in other 
words, radicles may theoretically be derived from aromatic 



344 HOMOLOGUES OP BENZENE 

hydrocarbons by taking away atoms of hydrogen. These 
radicles have no actual existence, but the assumption is useful 
in naming aromatic compounds; the mono- and di-substitution 
products of benzene, for example, may be regarded as com- 
pounds of the monovalent radicle phenyl, C 6 H 5 -, or of the 
divalent radicle pheni/lene, C 6 H 4 <, respectively, as in 
phenylamine (aniline), C 6 H 5 -NH 2 , and in o-, m- and jp-phenyl- 
enediamine, C 6 H 4 (NH 2 ) 2 . Toluene derivatives, again, may 
be named as if they were derived from the radicle toluyl, 
CH 3 -C 6 H 4 -, or from the radicle benzyl, C 6 H 5 -CH 2 -, according 
as hydrogen of the nucleus, or of the side-chain, has been 
displaced. The compound C 6 H 5 -CH 2 -OH, for example, is 
called benzyl alcohol. The isomeric hydroxy-compounds, 
C 6 H 4 (CH 3 )-OH, however, are usually known as the (o.m.p.) 
cresols (p. 408). Other hypothetical radicles, such as xylyl, 

f^TT 
C 6 H 3 (CH 3 ) 2 -, and xylylene, C 6 H 4 <C ri -rj 2 , are also made 

OJtlo 

use of. 

Toluene, methylbenzene, or phenylmethane, C 6 H 5 -CH 3 , 
although always prepared from the * 90 per cent, benzol ' 
separated from coal-tar (p. 307), can be obtained by any of 
the general reactions given above, and also by the dry 
distillation of balsam of Tolu (hence the name toluene) and 
other resins. 

Commercial toluene is invariably impure, and when shaken with 
concentrated sulphuric acid it colours the acid brown or black. It 
may be purified by repeated fractional distillation, but even then it 
will contain thiotolene, C 5 H 6 S, a hornologue of thiopliene (p. 310), 
and will show the indophenin reaction (with isatin and concen- 
trated sulphuric acid). 

Pure toluene is most conveniently prepared from balsam of 
Tolu, or by distilling pure toluic acid with lime, 

C 6 H 4 (CH 3 >COOH - C 6 H 5 .CH 3 + C0 2 . 

It is a mobile liquid of sp. gr. 0-882 at 0, and boils at 
110; it does not solidify even at - 28, and cannot, therefore, 



AND OTHER HYDROCARBONS. 345 

like benzene, be purified by freezing. It resembles benzene 
very closely in most respects, differing from it principally in 
those properties which are due to the presence of the methyl- 
group. Its behaviour with nitric acid and with sulphuric 
acid, for example, is similar to that of benzene, inasmuch as 
it yields nitro- and sulphonic-derivatives ; these compounds, 
moreover, exist in three isomeric (o.m.p.) forms, since they 
are di-substitution products of benzene. The presence of the 
methyl-group, on the other hand, causes toluene to show in 
some respects the properties of a paraffin. The hydrogen 
of this methyl-group may be displaced by chlorine, for 
example, and the latter by a hydroxyl- or amido-group, by 
methods exactly similar to those employed in bringing about 
similar changes in fatty compounds, substances such as 
C 6 H 5 .CH 2 C1, C 6 H 5 .CH 2 .OH, and C 6 H 5 -CH 2 .NH 2 being 
obtained. This behaviour was of course to be expected, since 
toluene or phenylmethane is a mono-substitution product of 
marsh-gas just as much as a derivative of benzene. 

The next homologue of toluene namely, the hydrocarbon 
of the molecular formula C 8 H 10 exists in the following four 
isomeric forms, of which the three xylenes or dimethylbenzenes 
are the most important, 



I I 

CH 3 

Ortho-xylene. Meta-xylene. Para-xylene. Elhylbenzene. 

The three xylenes occur in coal-tar, and may be partially 
separated from the other constituents of ' 50 per cent, benzol ' 
(p. 307) by fractional distillation. The portion boiling at 
136-141, after repeated distillation contains a large quantity 
(up to 85 per cent.) of m-xylene and smaller quantities of the 
o- and ^-compounds ; the three isomerides cannot be separated 







346 HOMOLOGUES OF BENZENE 

from one another or from all impurities by further distilla- 
tion, or by any simple means, although it is possible to obtain 
a complete separation by taking advantage of differences in 
chemical behaviour. 

7/i-Xylene is readily separated from the other isomerides by digest- 
ing with dilute nitric acid, which oxidises o- and ^?-xylene to the 
corresponding toluic acids, C 6 H 4 (CH 3 )-COOH, hut does not readily 
attack w-xylene ; the product is rendered alkaline by the addition 
of potash, and the unchanged hydrocarbon purified by distilla- 
tion in steam and fractionation. The isolation of o- and ^?-xylene 
depends on the following facts : (1) When crude xylene is agitated 
with concentrated sulphuric acid, o- and m-xylene are converted 
into sulphonic acids, C 6 H 3 (CH 3 ) 2 -SO 3 H ; jt?-xylene remains un- 
changed, as it is only acted on by fuming sulphuric acid. (2) The 
sodium salt of 0-xylenesulphonic acid is less soluble in water 
than the sodium salt of m-xylenesulphonic acid ; it is purified 
by recrystallisation, and converted into o-xylene by heating with 
hydrochloric acid under pressure (p. 394). 

The three xylenes may all be prepared by one or other 
of the general methods; when, for example, methyl chloride 
is passed into benzene in presence of aluminium chloride, 
o-xylene and a small quantity of the ^-compound are obtained, 

C 6 H 6 + 2CH 3 C1 = C 6 H 4 (CH 3 ) 2 + 2HC1 ; 

toluene, under the same conditions, yields the same two 
compounds, 

C 6 H 5 .CH S + CH 3 C1 = C 6 H 4 (CH 3 ) 2 + HC1. 

The non-formation of w-xylene in these two cases shows that 
the methyl-group first introduced into the benzene molecule 
exerts some directing influence on the position taken up by 
the second one (p. 364). 

Orthoxylene is obtained in a state of purity by treating 
o-bromotoluene with methyl iodide and sodium, 

PTT PTT 

C 6 H 4 <rp + CH 3 T + 2Na - C 6 H 4 <^ 3 + ffaBr + Nal, 

3 

pure paraxylene being produced in a similar manner from 
jp-bromotoluene ; metaxylene cannot be prepared by treating 



AND OTHER HYDROCARBONS. 347 

w-bromotoluene with methyl iodide and sodium, but is easily 
obtained in a pure condition by distilling mesitylenic acid 
(p. 328) with lime, 

C 6 H 3 (CH 3 ) 2 .COOH = C 6 H 4 (CH 3 ) 2 + C0 2 . 

The three xylenes are very similar in physical properties 
(compare p. 342), being all mobile, rather pleasant-smelling, 
inflammable liquids (j>-xylene melts at 15), which distil 
without decomposing, and are readily volatile in steam. They 
also resemble one another in chemical properties, although in 
some respects they show important differences, which must 
be ascribed to their difference in constitution. On oxidation, 
under suitable conditions, they are all converted in the first 
place into monocarboxylic acids which are represented by the 
formulae, 

CH 3 

-COOH 

COOH 

\ 

I 

COOH 
Ortho-toluic Acid. Meta-toluic Acid. Para-toluic Acid. 

On further oxidation the second methyl-group undergoes 
a like change, and the three corresponding dicarboxylic acids, 
C 6 H 4 (COOH) 2 , are formed (p. 436). 

The three hydrocarbons show slight differences in behaviour on 
oxidation, one being more easily acted on than another by a par- 
ticular oxidising agent. With chromic acid, for example, o-xylene 
is completely oxidised to carbon dioxide and water, whereas 
wi-xylene and jo-xylene yield the dicarboxylic acids (see above) ; 
with dilute nitric acid o-xylene gives o-toluie acid, and jo-xylene, 
p-toluic acid, but m-xylene is not readily acted on. Their be- 
haviour with sulphuric acid is also different (p. 346). 

Etliylbenzene, or plienylethane, C 6 H 5 -C H 5 , an isoineride 
of the xylenes, is not of much importance ; it occurs in 
coal-tar, and may be obtained by the general methods. 






348 HOMOLOGUES OF BENZENE 

It is a colourless liquid, boiling at 134, and on oxidation 
with dilute nitric acid or chromic acid it is converted into 
benzoic acid, 

C 6 H 5 .CH 2 -CH 3 + 60 = C 6 H 5 -COOH + C0 2 + 2H 2 0. 

The next member of the series has the molecular formula 
C 9 H 12 , and exists, as already pointed out (p. 339), in eight 
isomeric forms, of which the three trimethylbenzenes and 
isopropylbenzene are the most important. 

Mesitylene, 1:3:5- or symmetrical trimethylbenzene, 

CH 3 




CH 3 -L J-CH 3 



occurs in small quantities in coal-tar, but is most con- 
veniently prepared by distilling a mixture of acetone (2 
vols.), concentrated sulphuric acid (2 vols.), and water 
(1 vol.), sand being added to prevent frothing, 
3(CH 3 ) 2 CO = C 6 H 3 (CH 3 ) 3 + 3H 2 0. 

The formation of mesitylene in this way is of interest not only 
because it affords a means of synthesising the hydrocarbon from its 
elements, but also because it throws light on the constitution of 
the compound. Although the change is a process of condensation, 
and is most simply expressed by the graphic equation already given 
(p. 333), it might be assumed that the acetone is first converted 
into CH 3 -C i CH, or into CH 3 -C(OH): CH 2 (by intramolecular change), 
and that mesitylene is then produced by a secondary reaction ; 
whatever view, however, is adopted as to the actual course of the 
reaction (unless, indeed, highly improbable assumptions be made), 
the final result is always the same, and the constitution of the 
product is best expressed by a symmetrical formula ; for this 
and other reasons, mesitylene is regarded as symmetrical or 1:3:5- 
trimethyl benzene. 

Mesitylene is a colourless, mobile, pleasant-smelling liquid, 
boiling at 164-5, and volatile in steam; when treated with 
concentrated nitric acid it yields mono- and di-nitromesityl- 
ene, whereas with a mixture of nitric and sulphuric acids it 



AND OTHER HYDROCARBONS. 349 

is converted into trinitromesitylene, C 6 (]Sr0 ) 3 (CH 3 ) 3 . On 
oxidation with dilute nitric acid it yields mesitylenic acid, 
C 6 H 3 (CH 3 ) 2 .COOH ; uvitic add, C 6 H 3 (CH 3 )(COOH) 2 ; and 
trimesic acid, C 6 H 3 (COOH) 3 , by the transformation of suc- 
cessive methyl- into carboxyl-groups. 

Pseudocumene, or l:2:4-trimethylbenzene, C 6 H 3 (CH 3 ) 3 , and hemi- 
mellitene, or l:2:3-trimethylbenzene, also occur in small quantities 
in coal-tar, and are very similar to mesitylene in properties ; on 
oxidation, they yield various acids by the conversion of one or 
more methyl- into carboxyl-groups. 

Cumene, or isopropylbenzene, C 6 H 5 -CH(CH 3 ) 2 , is usually 
obtained from coal-tar ; it may be prepared in a pure condi- 
tion by distilling cumic acid (isopropylbenzoic acid) with lime, 

- 



by treating a mixture of isopropyl bromide and benzene with 
aluminium chloride, 

C 6 H 6 + C 3 H 7 Br = C 6 H 5 .C 3 H 7 + HBr, 

and by the action of sodium on a mixture of bromobenzene 
and isopropyl bromide, 

C 6 H 5 Br + C 3 H r Br + 2Na = C 6 H 5 .C 3 H 7 + 2NaBr. 

It is a colourless liquid, boiling at 153, and on oxidation 
with dilute nitric acid it is converted into benzoic acid. 

Cymene, or ^ara-methylisopropylbenzene, C 6 H 4 (CH 3 )-C 3 H 7 , 
is a hydrocarbon of considerable importance, as it occurs in 
the ethereal oils or essences of many plants ; it is easily pre- 
pared in many ways, as, for example, by heating camphor 
with phosphorus pentoxide or phosphorus pentasulphide, 

CioH 16 = C 10 H 14 + H 2 0, 

by heating turpentine with concentrated sulphuric acid or 
with iodine (both of which, in this case, act as oxidising 
agents), 



350 HOMOLOGUES OF BENZENE 

and by heating thymol (p. 409), or carvacrol (p. 410), with 
phosphorus pentasulphide (which acts as a reducing agent), 

C 6 H 3 (OH)<^ + 2H = C 6 H 4 <^L 3 +H 2 0. 
U 3 i r U 3 i r 

Cymene is a pleasant-smelling liquid of sp. gr. 0-8722 at 0, 
and boils at 175-176; on oxidation with dilute nitric acid 
it yields p-toluic acid, C 6 H 4 (CH 3 )-COOH, and terepMhalic 
acid, C 6 H 4 (COOH) 2 . 

Diphenyl, Diphenylmefhane, awl Triphenylmefhane. 

All the hydrocarbons hitherto described contain only one 
benzene nucleus, and may be regarded as derived from 
benzene by the substitution of fatty alkyl-groups for atoms 
of hydrogen ; there are, however, several other series of 
aromatic hydrocarbons, which include compounds of very 
considerable importance. 

Diphenyl, C 6 H 5 -C 6 H 5 , contains two benzene nuclei, and 
is the hydrocarbon in the aromatic series which corresponds 
with ethane in the fatty series, although it is not a homo- 
logue of benzene. It is formed on treating bromobenzene 
in ethereal solution with sodium, 

2C 6 H 5 Br + 2^"a = C 6 H 5 .C 6 H 5 + 2NaBr, 

the reaction being analogous to the formation of ethane 
(dimethyl) from methyl iodide by the action of sodium 
(Part I. p. 58). 

Diphenyl is prepared by passing benzene vapour through a 
red-hot tube filled with pieces of pumice (Berthelot), 



The dark-coloured distillate is fractionated, and the diphenyl 
purified by recrystallisation from alcohol. 

Diphenyl is a colourless, crystalline substance, melts at 
71, and boils at 254 ; when oxidised with chromic acid 
it yields benzoic acid, one of the benzene nuclei being 
destroyed. Its behaviour with halogens, nitric acid, and 



AND OTHER HYDROCARBONS. 351 

sulphuric acid is similar to that of benzene, substitution 
products being formed. 

Diphenylmethane, C 6 H 5 -CH 2 -C 6 H 5 , also contains two ben- 
zene nuclei ; it may be regarded as derived from marsh-gas 
by the substitution of two phenyl-gronps for two atoms of 
hydrogen, just as toluene or phenylmethane may be con- 
sidered as a mono-substitution product of methane. 

Diphenylmethane may be prepared by treating benzene with 
benzyl chloride (p. 361) in presence of aluminium chloride, 

C 6 H 6 + C 6 H 5 .CH 2 C1 -* C 6 H 5 .CH 2 .C 6 H 5 + HC1. 
It is a crystalline substance, and melts at 26-5 - } when 
treated with nitric acid it yields nitro-derivatives in the 
usual way, and on oxidation with chromic acid it is con- 
verted into diphenyl ketone or benzophenone, C 6 H 5 -CO-C 6 H 5 
(p. 424). 

Triphenylmethane, (C 6 H 5 ) 3 CH, is the parent substance 
of an important group of compounds all of which contain 
three benzene nuclei. It is formed when benzal chloride 
(p. 362) is treated with benzene in presence of aluminium 
chloride, 

C 6 H 5 -CHC1 2 + 2C 6 H 6 = (C 6 H 5 ) 3 CH + 2HC1, 

but it is usually prepared by heating a mixture of chloroform 
and benzene with aluminium chloride, 

CHC1 3 + 3C 6 H 6 = (C 6 H 5 ) 3 CH + 3HC1. 

Aluminium chloride (5 parts) is gradually added to a mixture 
of chloroform (1 part) and benzene (5 parts), which is then heated 
at about 60 until the evolution of hydrogen chloride ceases, an 
operation occupying about thirty hours ; after cooling and adding 
water, the oily product is separated and submitted to fractional 
distillation; those portions of the distillate which solidify on 
cooling consist of crude triphenylmethane, which is further purified 
by recrystallisation from benzene and then from ether. 

Triphenylmethane is a colourless, crystalline compound, 
which melts at 92, and boils at 358 ; it is readily soluble 
in ether and benzene, but only sparingly so in cold alcohol. 



352 HOMOLOGUES OF BENZENE, ETC. 

When treated with fuming nitric acid it is converted into 
a yellow, crystalline tfn'wfro-derivative, CH(C 6 H 4 -N0 2 ) 3 , 
which, like other nitro-componnds, is readily reduced to 
the corresponding triamido-eompoimd, CH(C 6 H 4 -]S T H 2 ) 3 ; the 
last-named substance is of considerable importance, as many 
of its derivatives are largely employed as dyes (p. 519). 

On oxidation with chromic acid, triphenylmethane is con- 
verted into triphenyl carbinol, (C 6 H 5 ) 3 C-OH. 



CHAPTER XXII. 

HALOGEN DERIVATIVES OF BENZENE AND ITS HOMOLOGUES. 

The action of halogens on benzene has already been re- 
ferred to (p. 313), and it has been pointed out that the 
hydrocarbon yields either additive or substitution products 
according to the conditions of the experiment; at ordinary 
temperatures, in absence of direct sunlight, substitution 
products are formed, the action being greatly hastened by 
the presence of a halogen carrier, such as iodine, iron, or 
antimony;* at its boiling-point, however, or in presence of 
direct sunlight, the hydrocarbon yields additive compounds 
by direct combination with six atoms of the halogen. 

The homologues of benzene also show a curious behaviour ; 
when treated with chlorine or bromine at ordinary tempera- 
tures in absence of direct sunlight, they are converted into 
substitution products by the displacement of hydrogen of 
the nucleus, and, as in the case of benzene itself, interaction 
is greatly promoted by the presence of a halogen carrier; 

* The action of iodine has been explained (Part I. p. 165) ; iron, antimony, 
molybdenum, and certain other metals act as halogen carriers, probably 
because they are converted into compounds (FeCl 3 , SbCl 5 , MoCl s ) which 
readily dissociate, yielding nascent halogen and lower halogen derivatives 
(FeCl 2 , SbCl 3 , MoCl 3 ) ; the latter then combine again with a fresh quantity 
of the halogen, and thus the processes are repeated. 



HALOGEN DERIVATIVES OF BENZENE, ETC. 353 

under these conditions toluene, for example, gives a mixture 
of o- and 7?-chlorotoluenes or bromotoluenes, 

C 6 H 5 .CH 3 + C1 2 = C 6 H 4 <^ +HC1. 

"When, on the other hand, no halogen carrier is present, 
and the hydrocarbons are treated at their boiling-points, 
or in direct sunlight, with chlorine or bromine, they yield 
derivatives by the substitution of hydrogen of the side-chain ; 
when, for example, chlorine is passed into 'boiling toluene, 
the three hydrogen atoms of the methyl-group are succes- 
sively displaced, benzyl chloride, C 6 H 5 -CH 2 C1, benzal chloride, 
C C H 5 .CHC1 2 , and benzotrichloride, C 6 H 5 -CC1 3 , being formed ; 
xylene, again, when heated at its boiling-point and treated 
with bromine, gives the compounds, 

n ,CH 2 Br n _ ,CH 2 Br 

C 6 H 4 < CH 2 3 and C 6 H 4 < CH ^ Br ' 

Although these statements are true in the main, it must 
not be supposed that substitution takes place only in the 
nucleus or side-chain, as the case may be, because this 
is not so; in presence of a halogen carrier traces of a 
halogen derivative are formed by substitution of hydrogen 
of the side-chain, and at the boiling-point of the hydro- 
carbon, or in direct sunlight, traces of substitution pro- 
ducts, formed by displacement of hydrogen of the nucleus, 
are obtained. 

Iodine seldom acts on benzene and its homologues under 
any of the above-mentioned conditions, partly because of the 
slight affinity of iodine for hydrogen, partly because the 
hydrogen iodide which is produced interacts with the-iodo- 
derivative, and reconverts it into the hydrocarbon, 



if, however, iodic acid, or some other substance which de- 
composes hydrogen iodide, be present, iodo-derivatives may 

Org. Chem. W 



354 HALOGEN DERIVATIVES OF BENZENE 

sometimes be prepared by direct treatment with the halogen 
at high temperatures.* 

Preparation. Chloro- and bromo-derivatives of benzene 
and its homologues may be prepared by direct ' clilorination ' 
or ' bromination,' the conditions employed depending on 
whether hydrogen of the nucleus or of the side-chain is to 
be displaced ; if, for example, it were desired to convert 
toluene into p-chloro'benzyl chloride, C 6 H 4 C1-CH 2 C1, the 
hydrocarbon might be first treated with chlorine at ordinary 
temperatures in presence of iodine, and the p-chlorotoluene, 
C 6 H 4 C1-CH 3 , after having been separated from the accom- 
panying ortho-compound, would then be heated to boiling in 
a flask connected with a reflux condenser, and a stream of 
dry chlorine led into it. 

In all operations of this kind the theoretical quantity, or a slight 
excess of halogen, is employed ; the bromine is weighed directly, 
but the weight of the chlorine is usually ascertained indirectly by 
continuing the process until the theoretical gain in weight has 
taken place ; the halogen should be dry, as in presence of water 
oxidation products of the hydrocarbon may be formed. The fumes 
of hydrogen chloride or bromide evolved during such operations are 
conveniently absorbed by passing them to the bottom of a deep 
vessel containing damp coke. 

A very important general method for the preparation of 
aromatic halogen derivatives, containing the halogen in the 
nucleus, consists in the decomposition of the diazo-compounds. 
As the properties and decompositions of the last-named 
substances are described later (p. 381), it is only necessary 
to state here that this method is used in the preparation 
of nearly all iodo-compounds, and that it affords a means 
of indirectly substituting any of the halogens, not only for 
hydrogen, but also for nitro- or amido-groups. 

* HIO 3 + 5HI = 3I 2 + 3H 2 O. lodo- substitution products are also fre- 
quently formed on employing FeCl 3 , or A1C1 3 , as a carrier, because the IC1 
which is formed has a much more energetic substituting action than the 
iodine itself, owing to the simultaneous formation of HC1, 

C 6 H 5 



AND ITS HOMOLOGUES. 355 

The conversion of benzene or toluene, for example, into a 
mono-halogen derivative by this method involves the follow- 
ing steps, 

C 6 H 6 -> C 6 H 5 .N0 2 -* C 6 H 5 .NH 2 C 6 H 5 -N 2 C1 -> C 6 H 5 C1 

Benzene. Nitrobenzene. Amidobenzene. Diazobenzene Chlorobenzene. 

Chloride. 



Toluene. Nitrotoluene. Aniidotoluene. Diazotoluene Broniotoluene. 

Bromide. 

The preparation of a ^'-halogen derivative may sometimes 
be carried out in a similar manner, the hydrocarbon being 
first converted into the cfo'-nitro-derivative j in most cases, 
however, it is necessary to prepare the mono-halogen, derivative 
by the reactions given above, and after converting it into 
the nitre-compound, the nitro-group is displaced by a second 
atom of halogen by repeating the series of operations, 

C 6 H 5 Br C fl H 4 < NO> C 6 H 4 < N 1 H2 - C 6 H 4 < N l 2C1 ->C 6 H 4 < cl r . 

Broino- Nitrobromo- Amidobromo- Diazobromo- Bromochloro- 

benzene. benzene. benzena benzene Chloride. benzene. 

Halogen derivatives of benzene and its homologues are some- 
times prepared by treating hydroxy-compounds with pentachloride 
or pentabromide of phosphorus, the changes being similar to those 
which occur in the case of fatty hydroxy-compounds; if the 
hydroxyl-group be present in the nucleus, the halogen naturally 
takes up the same position, phenol, for example, giving chloro- 
benzene, and cresol, chloro toluene, 

C 6 H 5 .OH + PC1 5 = C 6 H 5 C1 + POC1 3 + HC1 



an aromatic alcohol (p. 414), such as benzyl alcohol, also yields the 
corresponding halogen derivative (benzyl chloride), containing the 
halogen in the side-chain, 

C 6 H 5 .CH 2 -OH + PC1 5 = C 6 H 5 -CH 2 C1 + POC1 3 + HC1. 

Halogen derivatives may also be obtained by distilling halogen 
acids with lime, 

C 6 H 4 Br.COOH = C 6 H 5 Br + CO 2 , 



356 HALOGEN DERIVATIVES OF BENZENE 

by heating sulphonic chlorides (p. 394) with phosphorus penta 
chloride, 

C 6 H 5 -S0 2 C1 + PC1 5 = C 6 H 5 C1 + POC1 3 + SOC1 2 , 
and by several other methods of less importance. 

Properties. At ordinary temperatures, some of the halogen 
derivatives of benzene and its homologues are colourless 
liquids ; the majority, however, are crystalline solids. They 
are all insoluble, or nearly so, in water, but readily soluble 
in alcohol, ether, &c. Many are readily volatile in steam, 
and distil without decomposing, the boiling-point being 
higher and the specific gravity greater than that of the parent 
hydrocarbon, and rising also on substituting bromine for 
chlorine, or iodine for bromine. 

Benzene. Chlorobenzene. Bromobenzene. lodobenzene. 

B.p 80-5 132 155 188 

Sp.gr. at 0-899 1-128 1-521 1-857. 

They are not so inflammable as the hydrocarbons, and the 
vapours of many of them have a very irritating action on 
the eyes and respiratory organs. 

When the halogen is united with carbon of the benzene 
nucleus, it is, as a rule, very firmly combined, and cannot 
be displaced by the liydroxyl- or amido-group with the aid of 
aqueous potash, ammonia, or silver hydroxide ; such halogen 
derivatives, moreover, are not acted on by alcoholic potash, 
and cannot be converted into less saturated compounds in the 
same way as ethyl bromide, for example, may be converted 
into ethylene; in fact, no derivative of benzene containing 
less than six monovalent atoms, or their valency equivalent, 
is known. If, however, hydrogen of the nucleus has been 
displaced by one or more nitro-groups, as well as by a halogen, 
the latter often becomes much more open to attack ; o- and 
>-chloronitrobenzene, C 6 H 4 C1-N0 2 , for example, are moderately 
easily acted on by alcoholic potash and by alcoholic ammonia 
at high temperatures, yielding the corresponding nitro- 
phenols, C 6 H 4 (OH)-N0 2 , and nitranilines, C 6 H 4 (NH 2 )-N"0 2 ; 
w-chloronitrobenzene, however, is not acted on under these 



AND ITS HOMOLOGUES. 357 

conditions, a fact which shows that such isomerides sometimes 
differ very considerably in chemical properties. 

Halogen atoms in the side-chains are very much less firmly 
combined than those in the nucleus, and may be displaced by 
hydroxyl- or amido-groups just as in fatty compounds ; benzyl 
chloride, C 6 H 5 -CH 2 C1, for example, is converted into benzyl 
alcohol, C 6 H 5 -CH 2 -OH, by boiling sodium carbonate solution, 
and when heated with alcoholic ammonia it yields benzyl- 
amine, C 6 H 5 .CH 2 .NH 2 (p. 380). 

Halogen atoms in the nucleus, as well as those in the side- 
chain, are displaced by hydrogen on treatment with hydriodic 
acid and amorphous phosphorus at high temperatures, or 
with sodium amalgam in alcoholic solution ; the former, 
however, are much less readily displaced than the latter. 

Chlorobenzene, or phenyl chloride, C 6 H 5 C1, may be de- 
scribed as a typical example of those halogen derivatives in 
which the halogen is combined with carbon of the nucleus. 
It may be obtained (together with dichlorobenzenes, C 6 H 4 C1 2 , 
trichlorobenzenes, C 6 H 3 C1 3 , &c.) by chlorinating benzene ; also 
by treating phenol (p. 404) with phosphorus pentachloride, 
just as ethyl chloride may be produced from alcohol, 

C 6 H 5 .OH + PC1 5 - C 6 H 5 C1 + POC1 3 + HC1. 

It is usually prepared by Sandmeyer's reaction that is to say, 
by warming an aqueous solution of diazobenzene chloride with 
cuprous chloride (p. 383) ; this method, therefore, affords a 
means of preparing chlorobenzene, not only from the diazo- 
compound, but also indirectly from amidobenzene (aniline), 
nitrobenzene, and benzene, in the manner already indicated 
(p. 355). Chlorobenzene is a colourless, mobile, pleasant- 
smelling liquid, specifically heavier than water; it boils at 
132, and is readily volatile in steam. Like benzene, it is 
capable of yielding nitro-, amido-, and other derivatives by 
the displacement of one or more hydrogen atoms; it differs 
from ethyl chloride and from other fatty alkyl halogen com- 
pounds in being unacted on by water and alkalies, or by 



358 HALOGEN DERIVATIVES OP BENZENE 

metallic salts ; it is impossible, for example, to prepare phenyl 
acetate, CH 3 -COOC 6 H 5 , by treating silver acetate with chloro- 
benzene, although ethyl acetate is easily obtained from ethyl 
chloride in this way. 

Bromobenzene, or phenyl bromide, C 6 H 5 Br, may be pre- 
pared from diazobenzene sulphate by Sandmeyer's reaction, 
using cuprous bromide (p. 384)-; also by brominating benzene 
in presence of iron. 

Benzene (1 part) is placed in a flask, provided with a reflux 
condenser, together with a little iron wire, and the bromine 
(2 parts) is added gradually from a stoppered funnel, the bent stem 
of which passes through the cork of the flask ; the hydrogen 
bromide which is evolved is absorbed by leading it into a tower 
containing moist coke. The product is washed well with dilute 
caustic soda and water successively, dried, and separated from 
any unchanged benzene by fractional distillation. The p-dibromo- 
benzene (m.p. 89; h.p. 219), which is also formed in the above 
reaction, remains as a residue if the distillation be stopped when 
the thermometer rises to about 170; it solidifies on cooling, and 
may be recrystallised from aqueous alcohol. 

Bromobenzene is a colourless liquid, boiling at 155, and 
closely resembles chlorobenzene in all respects. As a rule, 
however, the bromo-derivatives crystallise more readily, and 
have a higher melting-point than the corresponding chloro- 
com pounds. 

lodobenzene, C 6 H 5 I, cannot be obtained by the action of 
iodine alone on benzene, but it is formed when the hydro- 
carbon is heated with iodine in presence of iodic acid at 
about 220 (p. 353) ; it is most conveniently prepared by 
decomposing diazobenzene sulphate with potassium iodide in 
aqueous solution, 

C 6 H 5 .N 2 HS0 4 + KI = C 6 H 5 I + KHS0 4 + N 2 . 

Aniline (1 part) is diazotised with sodium nitrite and sulphuric 
acid (compare p. 384), the cold solution of the diazo-sulphate 
poured into a concentrated solution of potassium iodide (2 parts), 
and the mixture gradually heated until nitrogen is no longer 
evolved ; the iodobenzene is then separated by steam distillation, 
washed with dilute caustic soda, dried, and distilled. 



AND ITS HOMOLOGUES. 359 



It is a heavy, colourless, mobile liquid, boiling at 188; 
when it is dissolved in chloroform and dry chlorine, passed 

Cl 

into the well -cooled solution, the dichloride C 6 H 5 I<Cpn 

separates in crystals (Willgerodt), the iodine becoming tri- 
valent, as it probably is in iodine trichloride, IC1 3 . 

lodobenzene dichloride is slowly decomposed by dilute 
caustic soda (4-5 per cent,), and if ground up with excess of 
such a solution, and left in contact with it for 6-8 hours, it is 
converted into iodosobenzene, 

C 6 H 5 IC1 2 + 2NaOH = C 6 H 5 IO + 2NaCl + H 2 0, 

which can be separated by nitration, washed with water, and 
dried on porous earthenware. 

Iodosobenzene, C 6 H 5 IO, is a colourless, amorphous sub- 
stance, moderately easily soluble in warm water and alcohol \ 
it explodes at about 210. It has basic properties, and unites 
with acids forming a salt and water, 

C 6 H 5 IO + 2C 2 H 4 2 = C 6 H 5 I(C 2 II 3 2 ) 2 + H 2 ; 

it is also an oxidising agent, and liberates iodine from 
potassium iodide in acid solution, 

C 6 H 5 IO + 2HI - C 6 H 5 I + 1 2 + H 2 0. 

When iodosobenzene is submitted to distillation in steam 
it undergoes a most interesting decomposition giving iodo- 
benzene, which distils over with the water, and iodoxybenzene, 
which is non-volatile, 



lodoxybenzene, C 6 H 5 I0 2 , separates in colourless needles 
when the aqueous solution is evaporated to a small volume 
and then allowed to cool ; it explodes when heated at 
about 230. Unlike iodosobenzene, it does not show basic 
properties,"" but it is an oxidising agent and liberates 
iodine (4 atoms) from hydriodic acid. 

When a mixture of iodosobenzene and iodoxybenzene is 



360 HALOGEN DERIVATIVES OF BENZENE 

shaken with water and freshly precipitated silver hydroxide, 
interaction takes place and diphenyliodonium iodate is formed, 

C 6 H 5 IO + C 6 H 5 I0 2 + AgOH = (C 6 H 5 ) 2 LI0 3 + AgOH. 

This product is the salt of a strongly basic hydroxide, 
(C 6 H 5 ) 2 LOH, diphenyliodonium hydroxide, which has only 
been isolated in the form of its salts ; it is an interesting fact 
that such derivatives of trivalent iodine should show basic 
properties. 

These remarkable compounds were discovered and investi- 
gated by Willgerodt and by V. Meyer ; analogous compounds 
have been obtained from other iodo-derivatives containing the 
iodine atom directly united with the benzene (or naphthalene) 
nucleus. 

Chlorotoluene, or toluyl chloride, C 6 H 4 C1-CH 3 , being a 
di-substitution product of benzene, exists in three isomeric 
modifications, only two of which namely, the o- and ^-com- 
pounds, are formed on treating cold toluene with chlorine in 
presence of iodine or iron ; the three isomerides may be 
separately prepared by treating the corresponding cresols 
(p. 408) with phosphorus pentachloride, 

C 6 H 4 <J 3 + PC1 5 = C 6 H 4 <cH 3 + POCI 3 + HC1, 

but they are best prepared from the corresponding toluidines 
by Sandmeyer's method, 



64 - 64 64 CH 

O O O 

Toluidine. Diazotoluene Chloride. Chlorotoluene. 

Orthochlorotoluene boils at 156, metachlorotoluene at 150, 
and parachlorotoluene at 160; they resemble chlorobenzene 
in most respects, but, since they contain a methyl-group, they 
have also some of the properties of fatty compounds; on 
oxidation, they are converted into the corresponding chloro- 
benzoic acids, C 6 H 4 C1-COOH, just as toluene is transformed 
into benzoic acid. 



AND ITS HOMOLOGUES. 361 

Benzyl chloride, C 6 H 5 -CH 2 C1, although isomeric with the 
three chlorotoluenes, differs from them very widely, and may 
be taken as an example of the class of halogen-compounds 
in which the halogen is present in the side-chain. It can 
be obtained by treating benzyl alcohol (p. 415) with phos- 
phorus pentachloride, 

C 6 H 5 .CH 2 .OH + PC1 5 - C 6 H 5 -CH 2 C1 + POC1 3 + HC1, 

but is always prepared by passing chlorine into boiling 
toluene, 

C 6 H 5 -CH 3 + C1 2 - C 6 H 5 .CH 2 C1 + HC1. 

The toluene is contained in a flask which is heated on a sand- 
bath and connected with a reflux condenser; a stream of dry 
chlorine is then passed into the boiling liquid until the theoreti- 
cal gain in weight has taken place and the product is purified 
by fractional distillation ; the action takes place most rapidly in 
strong sunlight. 

Benzyl chloride is a colourless, unpleasant-smelling liquid, 
boiling at 176; it is insoluble in water, but miscible with 
alcohol, ether, benzene, &c. It behaves like other aromatic 
compounds towards nitric acid, by which it is converted into 
a mixture of isomeric nitro-compounds, C 6 H 4 (N0 2 )-CH 2 C1. 
At the same time, however, it has many properties in 
common with the alkyl halogen compounds ; like ethyl 
chloride, it is slowly decomposed by boiling water, yield- 
ing the corresponding hydroxy-compound, benzyl alcohol 
(p. 415), 

C 6 H 5 .CH 2 C1 + H 2 = C 6 H 5 .CH 2 .OH + HC1, 

and just as ethyl chloride interacts with silver acetate, giving 
ethyl acetate, so benzyl chloride, under the same conditions, 
yields the ester, benzyl acetate, 

C 6 H 5 .CH 2 C1 + CH 3 -COOAg = CH 3 .COOCH 2 -C 6 H 5 + AgCl. 

Benzyl chloride is a substance of considerable commercial 
importance, inasmuch as it is used for the preparation of 
benzaldehyde (p. 418). 



362 HALOGEN DERIVATIVES OF BENZENE, ETC. 

Benzol chloride, C 6 H 5 -CHC1 2 , may be obtained by treating 
benzaldehyde with phosphorus pentachloride, 

C e H 6 .CHO + PC1 5 = C 6 H 5 .CHC1 2 + POC1 3 , 
but it is prepared by chlorinating toluene just as described 
in the case of benzyl chloride, except that the process is 
continued until twice as much chlorine has been absorbed. 
It is a colourless liquid, boiling at 206, and is extensively 
used for the preparation of benzaldehyde. 

Benzotrichloride, or phenylchloroform, C 6 H 5 -CC1 3 , is also 
prepared by chlorinating boiling toluene ; it boils at 213, and 
when heated with water it is converted into benzoic acid, 

C 6 H 5 .CC1 3 + 2H 2 = C 6 H 5 -COOH + 3HC1. 



CHAPTEK XXIII. 

NITRO-COMPOUNDS. 

It has already been stated that one of the most characteristic 
properties of aromatic compounds is the readiness with which 
they may be converted into nitro-derivatives by the substitu- 
tion of nitro-groups for hydrogen of the nucleus; the com- 
pounds formed in this way are of the greatest importance, 
more especially because it is from them that the amido- and 
diazo-compounds are prepared. 

Preparation. Many aromatic compounds may be ' nitrated ' 
that is to say, converted into their nitro-derivatives, by dis- 
solving them in concentrated nitric acid (sp. gr. 1-3 to 1-5), 
in the cold or at ordinary temperatures, and under such 
conditions a mononitro-compound is usually produced ; ben- 
zene, for example, yields nitrobenzene, and toluene, a mixture 
of o- and p-nitrotoluenes, 

C 6 H 6 + HN0 3 = C 6 H 5 .N0 2 + H 2 
C 6 H 5 -CH 3 + HN0 3 = CgH^CHgJvNOj + H 2 0. 



NITRO-COMPOUNDS. 363 

Some aromatic compounds, however, are insoluble in nitric 
acid, and are then only very slowly acted on ; in such cases 
a mixture of concentrated nitric and sulphuric acids is used. 
This mixture is also employed in many cases, even when 
the substance is soluble in nitric acid, because the sulphuric 
acid combines with the water which is produced during the 
interaction. When a large excess of such a mixture is used, 
and especially when heat is applied, the aromatic compound 
is usually converted into (a mixture of isomeric) dinitro- or 
trinitro-derivatives ; benzene, for instance, yields a mixture 
of three dinitro-benzenes, the principal product, however, 
being the meta-compound, 

C 6 H 6 + 2HISr0 3 = C 6 H 4 (N0 2 ) 2 + 2H 2 0. 



As soon as nitration is complete (portions of the product may be 
tested from time to time), the solution or mixture, having been 
cooled if necessary, is poured on to ice or into a large volume of 
water, and the product, which is usually precipitated in crystals, 
separated by filtration, or if an oil, by extraction with ether, or in 
some other manner. 

Generally speaking, the number of hydrogen atoms dis- 
placed by nitro-groups is greater the higher the temperature 
and the more concentrated the acid, or mixture of acids, 
employed, but depends to an even greater extent on the nature 
of the substance undergoing nitration, because the introduc- 
tion of nitro-groups is facilitated when other atoms or groups, 
especially alkyl radicles, have already been substituted for 
hydrogen of the nucleus. The nature of these atoms or groups 
determines, moreover, the position taken up by the entering 
nitre-group ; if the former be strongly negative or acid in 
character, as, for example, -N0 2 , -COOH, and -S0 3 H, a 
w-nitro-derivative is formed, whereas, when the atom or group 
in question is a halogen, an alkyl, or an amido- or hydroxyl- 
group, a mixture of the o- and j9-nitro-derivatives is produced. 

This directing influence of an atom or group already com- 
bined with the nucleus, on the position which is taken up by 
a second atom or group, is by no means restricted to the case 



364 NITROCOMPOUNDS. 

of nitro-compoimds, but is observed in the formation of all 
benzene substitution derivatives, except, of course, in that of 
the mono-substitution products ; so regularly, in fact, is this 
influence exercised that it is possible to summarise the course 
of those reactions which take place in the formation of the 
best-known di-derivatives in the following statements : 

The relative position taken up by the following atoms or 
groups, Cl, Br, N0 2 , S0 3 H, which are capable of directly 
displacing hydrogen of the nucleus, depends on the nature of 
the atom or group, A, already united with the nucleus. 

When A = 01, Br, I, NH 2 , OH, CH 3 (or other fatty alkyl), 
a jpara-compound is the principal product, but it is usually 
accompanied by smaller and varying quantities of the ortho- 
compound. 

When, on the other hand, 

A = N0 2 , COOH, S0 3 H, OHO, CO.CH 3 , ON, 

a raeta-derivative is the principal product, and only very 
small quantities of the ortho- and para-compounds are 
formed. 

These statements also hold good when two identical atoms 
or groups are introduced in one operation, since the change 
really takes place in two stages ; when benzene, for example, 
is treated with nitric acid, meta-dinitrobenzene is the principal 
product, whereas with bromine it yields para-dibromobenzene. 

Properties. As a rule, aromatic nitro-compounds are 
yellowish, well-defined, crystalline substances, and are, there- 
fore, of great service in identifying hydrocarbons and other 
liquids; many of them are volatile in steam, but, with the 
exception of certain mono-nitro-derivatives, cannot be dis- 
tilled under ordinary pressure, as when heated strongly they 
undergo decomposition, sometimes with explosive violence ; 
they are generally insoluble in water, but soluble in benzene, 
ether, alcohol, &c. As in the case of the nitro-paraffins 
(Part I. p. 184), the nitro-group is very firmly combined, 
and is not, as a rule, displaced by the hydroxyl-group on 



NITRO-COMPOUNDS. 365 

treatment with aqueous or alcoholic potash even at high 
temperatures. 

The most important reaction of the nitre-compounds 
namely, their behaviour on reduction, is described later 
(p. 368). 

Nitrobenzene, C 6 H 5 -N0 2 , is usually prepared in the labora- 
tory by slowly adding to benzene (10 parts) a mixture of 
nitric acid of sp. gr. 1-45 (12 parts) and concentrated 
sulphuric acid (16 parts), the temperature being kept below 
about 40 by cooling in water. 

The nitrobenzene separates at the surface as a yellow oil, which 
takes up the benzene, so that it is necessary to bring the latter 
into contact with the acid mixture by giving the vessel a rotatory 
motion. As soon as all the benzene has been added, the mixture is 
heated at about 80 for half-an-hour, then cooled, and poured into 
a large volume of water ; the nitrobenzene, which collects at the 
bottom of the vessel, is separated with the aid of a funnel, washed 
with a little water or dilute soda until free from acid, dried with 
anhydrous calcium chloride, and fractionated, in order to separate 
it from unchanged benzene and from small quantities of dinitro- 
benzene which may have been produced ; this is very easily accom- 
plished, as the boiling-points of the three compounds are widely 
different. 

On the large scale, nitrobenzene is prepared in a similar manner, 
the operation being carried out in iron vessels provided with an 
arrangement for stirring, and the product is distilled from iron 
retorts, or, better, in a current of steam. 

Nitrobenzene is a pale-yellow oil of sp. gr. 1-2 at 20, and 
has a strong smell, which is very like that of benzaldehyde 
(p. 418) ; it boils at 205, is volatile in steam, and is miscible 
with organic liquids, but practically insoluble in water ; in 
spite of the fact that it is poisonous, it is often employed 
instead of oil of bitter almonds for flavouring and per- 
fuming purposes, under the name of 'essence of mirbane;' 
its principal use, however, is for the manufacture of aniline 
(p. 373). 

Meta-dinitrobenzene, C 6 H 4 (N0 2 ) 2 , is obtained, together 
with small quantities of the o- and^)-dinitro-compounds, when 



366 NITRO-COMPOUNDS. 

nitrobenzene (1 part) is gradually added to a mixture of 
nitric acid (sp. gr. 1-5; 1J parts) and concentrated sulphuric 
acid (1|- parts), and the whole then heated on a sand-bath, 
until a drop of the oil, which floats on the surface, solidifies 
completely when stirred with cold water. 

After cooling, the mixture is poured into a large volume of water, 
the solid product separated by filtration, washed with water, and 
recrystallised from hot alcohol until its melting-point is constant ; 
the o- and jo-compounds, formed only in very small quantities, 
remain dissolved in the mother-liquors. 

Meta-dinitrobenzene crystallises in pale-yellow needles, melts 
at 90, and is volatile in steam ; it is only sparingly soluble 
in boiling water, but dissolves freely in most organic liquids. 
On reduction with alcoholic ammonium sulphide (p. 369) it 
is first converted into m-nitraniline (p. 375), and then into 
w-phenylenediamine or meta-diamidobenzene, C 6 H 4 (NH 2 ) 2 
(p. 376). 

o-D'mitrobenzem and p-dinitrobenzene are colourless, crystal- 
line compounds, melting at 118 and 173 respectively; they 
resemble the corresponding w-compound in their behaviour 
on reduction, and in most other respects. o-Dinitrobenzene, 
however, differs notably from the other two isomerides, inas- 
much as it interacts with boiling soda, yielding o-nitrophenol 
(p. 405), and, with alcoholic ammonia at moderately high 
temperatures, giving o-nitraniline (p. 375). A similar be- 
haviour is observed in the case of other o-dinitro-compounds, 
the presence of the one nitro-group rendering the other more 
easily displaceable. 

Symmetrical trinitrobenzene, C 6 H 3 (N0 2 ) 3 , is formed when 
the w-dinitro-compound is heated with a mixture of nitric and 
anhydrosulphuric acids ; it crystallises in colourless plates 
and needles, melting at 121-122. 

The halogen derivatives of benzene are readily nitrated, 
yielding, however, the o- and ^-mononitro-derivatives only, 
according to the general rule ; the m-nitro-halogen compounds 
are therefore prepared by chlorinating or brominating nitro- 



NITRO-COMPOUNDS. 367 

benzene. All these nitre-halogen derivatives are crystalline, 
and, as will be seen from the following table, their melting- 
points exhibit the regularity already mentioned (p. 342), 
except in the case of m-iodonitrobenzene. 



Ortho. Meta. Para. 
o 



Chloronitrobenzene, C 6 H 4 Cl-ISr0 2 , 32-5 444 
Bromonitrobenzene, C 6 H 4 Br-N0 2 , 41-5 56 126 
lodonitrobenzene, C 6 H 4 LN0 2 , 49 33 171 

They are, on the whole, very similar in chemical properties, 
except that, as already pointed out (p. 356), the o- and p- 
compounds differ from the m-compounds in their behaviour 
with alcoholic potash and ammonia, a difference which recalls 
that shown by the three dinitrobenzenes. 

The nitrotoluenes, C 6 H 4 (CH 3 )-N0 2 , are important, because 
they serve for the preparation of the toluidines (p. 376). The 
o- and p-compounds are prepared by nitrating toluene, and may 
be partially separated by fractional distillation ; o-nitrotoluene 
melts at 10-5 and boils at 218, whereas p-nitrotoluene melts 
at 54 and boils at 230. m-Nitrotoluene is not easily pre- 
pared; it melts at 16, and boils at 230. 

Many other nitre-compounds are mentioned later. 



CHAPTER XXIV. 

AMIDOCOMPOUNDS AND AMINES. 

The hydrogen atoms in ammonia may be displaced by 
aromatic radicles, bases, such as aniline, C 6 H 5 'NH 2 , benzyl- 
amine, C 6 H 5 -CH 2 -NH 2 , and diamidobenzene, C 6 H 4 (NH 2 ) 2 , 
which are analogous to, and have many properties in common 
with, the fatty amines, being produced ; as, however, those 
compounds which contain the amido-group directly united 
with carbon of the nucleus differ in many important respects 
from those in which this group is present in the side-chain, 



368 AMIDO-COMPOUNDS AND AMINES. 

the former are usually called amido-compounds, whereas the 
latter are classed as aromatic amines, because they are the 
true analogues of the fatty amines. 

A mido-compo unds. 

The amido-compounds may, therefore, be regarded as 
derived from benzene and its homologues by the substitution 
of one. or more amido-groups for hydrogen atoms of the 
nucleus ; they may be classed as mono-, di-, tri-, &c. } amido- 
compounds, according to the number of such groups which 
they contain. 



C 6 H 4 (NH 2 ) 2 C 6 H 3 (NH 2 ) 3 . 

Amidobenzene (Aniline). Diamidobenzene. Triainidobenzeiie. 

With the exception of aniline, all amido-compounds exist in 
three or more isomeric modifications ; there are, for example, 
three isomeric (o.m.p.) diamidobenzenes, and three isomeric 
(o.m.p.) amido toluenes, or toluidines, C 6 H 4 (CH 3 )-NH 2 , a 
fourth isomeride of the toluidines namely, benzylamine, 
C 6 H 5 .CH 2 .NH 2 (p. 380) being also known. 

Preparation. The amido-compounds are almost always 
prepared by the reduction of the nitro-compounds ; various 
reducing agents, such as tin, zinc, or iron, and hydrochloric 
or acetic acid, are employed, but perhaps the most common 
one is a solution of stannous chloride in hydrochloric acid, 

C 6 H 5 -N0 2 + 6H = C 6 H 5 .NH 2 + 2H 2 

C 6 H 4 (CH 8 ).ff0 2 + 6H = C 6 H 4 (CH 3 )-NH 2 + 2H 2 

C 6 H 5 .N0 2 + 3SnCl 2 + 6HC1 = C 6 H 5 -NH 2 + 3SnCl 4 + 2H 2 0. 

Reduction is usually effected by simply treating the nitro-com- 
pound with the reducing mixture without a special solvent, when 
a vigorous reaction often ensues, heating being seldom necessary 
except towards the end of the operation. The solution contains the 
amido-compound, combined as a salt with the acid which has been 
employed ; when, however, tin or stannous chloride and hydro- 
chloric acid have been used, a double salt of the hydrochloride of 
the base and stannic chloride is produced ; in the reduction of nitro- 
benzene, for example, the double salt, aniline stannichloride, has 



AMIDO-COMPOUNDS AND AMINES. 369 

the composition (C 6 H 5 -NH 2 , HC1) 2 , SnCl 4 . The amido-compound 
is liberated by adding excess of caustic soda or lime, and distilled 
with steam, extracted with ether, or isolated in some other manner 
suitable to the special case. 

The reduction of mtro-compounds takes place in two stages : in 
the first there is produced an unstable derivative of hydroxylamirie, 



which, by the further action of the reducing agent, is converted 
into the amido-compound. 

p-Phenylhydroxylamine is a crystalline substance, melting at 81, 
and, like hydroxylamine, it is a base and forms salts such as the 
hydrochloride C 6 H 5 -NH-OH, HCI. When oxidised with potassium 
dichromate and dilute sulphuric acid, it yields nitrosobenzene, 
C 6 H 5 -NO, a crystalline, very volatile substance, melting at 68, 
which on oxidation is converted into nitrobenzene, and on reduc- 
tion, into aniline. 

Nitro-com pounds may also be reduced to amido-compounds 
by employing hydrogen sulphide in alkaline solution, or, more 
conveniently, an alcoholic solution of ammonium sulphide, 
C 6 H 5 .N0 2 + 3SH 2 = C 6 H 6 -NH 2 + 2H 2 + 3S. 

The nitro- compound is dissolved in alcohol, concentrated 
ammonia added, and a stream of hydrogen sulphide passed into 
the solution, until reduction is complete, heat being applied if 
necessary. The solution is then filtered from precipitated sulphur, 
the alcohol distilled off, and the residue acidified with hydro- 
chloric acid ; the filtered solution of the hydrochloride of the base 
is now evaporated to a small bulk and treated with soda, when the 
base separates as an oil or solid, and may then be purified by 
distillation, recrystallisation, &c. 

When there are two or more nitre-groups in a compound, 
partial reduction may be accomplished either by treating its 
alcoholic solution with the calculated quantity of stannous 
chloride and hydrochloric acid, or by adding strong ammonia 
and passing hydrogen sulphide ; in the latter, as in the former 
case, one nitro-group is reduced before a second is attacked, 
so that by stopping the current of gas at the right time 
(sometimes ascertained by finding the increase in weight), 
only partial reduction takes place. Dinitrobenzeno, for 

Org. Chem. X 



370 AMIDO-COMPOUNDS AND AMINES. 

example, can be converted into nitraniline by either of these 
methods, the latter being the more convenient, 

C fl H 4 <** + 3SH 2 = C 6 H 4 <]*? + 2H 2 + 3S. 

The amido-derivatives of toluene, xylene, &c. are prepared 
commercially by heating the hydrochlorides of the isomeric 
alkylanilines, such as methylaniline and dimethylaniline 
(p. 378), at 280-300, when the alkyl-group leaves the 
nitrogen atom and enters the nucleus, 

PTT 

H, HC1 -. CH 



Methylaniline Hydrochloride. p-Toluidiue Hydrochloride. 

In the case of dimethylaniline the change takes place in 
two stages, which may be represented as follows, 



C 6 H 5 .N(CH 3 ) 2 _ 

v ^ \NH 2 

Dimethylaniline. Methyl-p-toluidine. Xylidine. 

in this remarkable isomeric change the alkyl-group displaces 
hydrogen from the ortho- and from the para- position to the 
amido-group, but principally the latter; meta-derivatives cannot 
be prepared in this way. 

The diamido-compounds, such as the 0-, m-, and ^-diamido- 
benzenes or phenylenediamines, C 6 H 4 (NH 2 ) 2 , are prepared 
by reducing either the corresponding dinitrobenzenes, 
C 6 H 4 (N0 2 ) 2 , or the nitranilines, C 6 H 4 (N0 2 )-NH 2 , generally 
with tin and hydrochloric acid. 

Properties. The monamido-compounds are mostly colour- 
less liquids, which distil without decomposing, and are 
specifically heavier than water ; they have a faint but charac- 
teristic odour, and dissolve freely in alcohol, ether, and other 
organic solvents, but they are only sparingly soluble or in- 
soluble in water ; on exposure to air and light they darken, 
and ultimately become brown or black. 

They are comparatively weak bases, and are neutral to 
litmus, in which -respect they differ from the strongly basie 



AMIDO-COMPOUNDS AND AMINES. 371 

fatty amines and from the true aromatic amines, such as 
benzylamine (p. 380) ; nevertheless they combine with acids 
to form salts, such as aniline hydrochloride, C 6 H 5 -NH 2 , HC1, 
which, however, are readily decomposed by weak alkalies or 
alkali carbonates, with liberation of the bases. 

It will be seen, therefore, that the substitution of the 
phenyl radicle, C 6 H 5 -, for one of the hydrogen atoms in 
ammonia has the effect of diminishing or partially neutralis- 
ing the basic character of the latter, a result which is directly 
the opposite of that arrived at by displacing the hydrogen 
atoms of ammonia by an alkyl (or positive) group, since the 
amines are stronger bases than ammonia ; for this and other 
reasons (p. 403) the hypothetical phenyl-group is regarded 
as a negative or acid radicle. 

When two hydrogen atoms in ammonia are displaced by phenyl- 
groups, as in diphenylamine, (C 6 H 5 ) 2 NH (p. 379), the product is so 
feebly basic that its salts are decomposed by water. Triphenyl- 
amine, (C 6 H 5 ) 3 N (p. 380), moreover, does not form salts at all. 

For the same reason the hydroxy-, nitro-, and halogen-derivatives 
of the amido -compounds, such as amido-phenol, C 6 H 4 (OH)-NH 2 , 
nitraniline, C 6 H 4 (N0 2 )-NH 2 , chloraniline, C 6 H 4 C1-NH 2 , &c., are even 
weaker bases than the amido-compounds themselves, because the 
presence of the negative group or atom, HO-, N0 2 -, C1-, &c., 
enhances the acid character of the phenyl radicle. 

The amido-compounds differ from the fatty primary amines 
and from the true aromatic primary amines in their remark- 
able behaviour with nitrous acid. Although when warmed 
with nitrous acid in aqueous solution they yield phenols by 
the substitution of hydroxyl for the amido-group, just as 
the fatty amines under similar treatment are converted into 
alcohols (Part I. p. 207), 

C 6 H 5 .NH 9 + N0 2 H - C 6 H 5 .OH + N 2 + H,0 

C 2 H 5 .NH 2 + N0 2 H = C 2 H 5 -OH + N 2 + H 2 0, 

yet when treated with nitrous acid in cold aqueous solution, 

they are converted into diazo-compounds (p. 381), substances 

which are not produced from the primary amines. 



372 AMIDO-COMPOUNDS AND AMINES. 

It will be evident from the above statements that there are 
several important differences between the amido-compounds 
and the true primary amines, the character of an amido- 
group in the nucleus being influenced by its state of combina- 
tion ; nevertheless, except as regards those points already 
mentioned, amido-compounds have, on the whole, properties 
very similar to those of the true primary amines. 

The amido-compounds, like the primary amines, interact 
readily with alkyl halogen compounds, yielding alkyl-deriva- 
tives, such as methylaniline, C 6 H 5 -NH-CH 3 , dimethylaniline, 
C 6 H 5 -N(CH 3 ) 2 , &c., and also compounds such as phenyl- 
trimethylammonium iodide, C 6 H 5 -N(CH 3 ) 3 I, which corre- 
spond with the quaternary ammonium salts (Part I. p. 210). 

They are also readily acted on by acid chlorides and 
anhydrides, and even by acids on prolonged heating, yielding 
substances such as acetanilide and acetotoluidide, which are 
closely allied to the fatty amides (Part I. p. 164), and from 
which they may be regarded as derived, 

C 6 H 5 .NH 2 + CH 8 .COC1 = C 6 H 5 .NH-CO.CH 3 + HC1 
C 6 H 4 (CH 3 ).NH 2 + (CH 3 .CO) 2 = 

P -ToMdine. C 6 H 4 (CH 8 ).NH.CO.CH 8 + CH 3 .COOH ; 

Aceto-p-toluidide. 

these compounds are crystalline, and serve for the identifica- 
tion of the (liquid) amido-compounds ; like the amides, they 
are generally resolved into their constituents when boiled 
with acids or alkalies, 



The amido-compounds, like the fatty primary amines, give 
the carbylamine reaction ; when a trace of aniline, for example, 
is heated with alcoholic potash and chloroform, an intensely 
nauseous smell is observed, due to the formation of phenyl- 
carbylamine (Part I. pp. 207, 294), 

CH.ira + CHC1 + 3KOH = CH-N i C + 3KC1 + 3H 2 O. 



AMIDO-COMPOUNDS AND AMINES. 373 

Diamido- and trlamido-compounds, such as the three (o. m.%).) 
phenylenediamines or diamidobenzenes, C 6 H 4 (NH 2 ) 2 , and the 
triamidobenzenes, C 6 H 3 (NH 2 ) 8 , are very similar to the mon- 
amido-compounds in chemical properties, but differ from them 
usually in being solid, more readily soluble in water, and less 
volatile ; the triamido-compounds generally form salts, such 
as C 6 H 3 (NH 2 ) 3 , 2HC1, with only two equivalents of an acid. 

Aniline and its Derivatives. 

Aniline, amidobenzene, or phenylamine, C 6 H 5 -IS[H 2 , was 
first prepared by Unverdorben in 1826 by distilling indigo, 
the name aniline being derived from anil, the Spanish for 
indigo. Runge in 1834 showed that aniline is contained in 
small quantities in coal-tar, but its preparation from nitro- 
benzene was first accomplished by Zinin in 1841. 

Aniline is manufactured on a very large scale by the reduc- 
tion of nitrobenzene with scrap iron and crude hydrochloric 
acid ; but in preparing small quantities in the laboratory, the 
most convenient reducing agent is tin and hydrochloric acid, 

C 6 H 5 .N0 2 + 6H = C 6 H 5 -NH 2 + 2H 2 0, 
2C 6 H B -N0 2 + 3Sn + 12HC1 = 2C 6 H 5 -NH 2 + 3SnCl 4 + 4H 2 0. 

Nitrobenzene (50 grams) and granulated tin (80 grams) are placed 
in a flask, and concentrated hydrochloric acid (290 grams) added 
in small quantities at a time ; at first the mixture must he cooled 
if the reaction be too violent, hut when all the acid has been added, 
the product is gently heated on a water-bath until drops of nitro- 
benzene are no longer visible. The solution of aniline stanni- 
chloride is now treated with soda until strongly alkaline, the 
liberated aniline distilled in steam, and, after saturating the dis- 
tillate with salt, the base is separated with the aid of a funnel, 
dried over solid potash, and purified by distillation. 

Aniline is a poisonous oil, boiling at 184 ; it has a faint, 
characteristic odour, and is sparingly soluble in water, but 
readily in alcohol and ether ; it gradually turns yellow when 
exposed to light and air, becoming ultimately almost black. 
Although neutral to litmus, aniline has very decided basic 
properties, and neutralises acids, forming soluble salts, such 



374 AMIDO-COMPOUNDS AND AMINES. 

as aniline hydrocliloride, C 6 H 5 -NH. ? , HC1, and the rather 
sparingly soluble sulphate, (C^-NH^ H 2 S0 4 . The 
former, like the hydrochlorides of ethylamine, &c., forms 
double salts with platinic and auric chlorides ; on treating a 
moderately concentrated solution of the hydrochloride with 
platinic chloride, for example, the platinichloride, 

(C 6 H 5 .NH 2 ) 2 , H 2 PtCl 6) 

is precipitated in yellow plates, which are moderately soluble 
in water. 

When aniline (one drop *) is heated with chloroform and 
alcoholic potash it yields phenylcarbylamine, C 6 H 5 -N!C, a 
substance readily recognised by its extremely disagreeable 
odour; the presence of aniline may also be detected by 
treating its aqueous solution with bleaching-powder solution 
or sodium hypochlorite, when an intense purple colouration 
is produced. 

When solutions of the salts of aniline are treated with 
nitrous acid, at ordinary temperatures, salts of diazo-com- 
pounds (p. 381) are formed ; but on warming, the latter are 
decomposed with formation of phenol (p. 404). 

Aniline is very largely employed in the manufacture of 
dyes, and in the preparation of a great number of benzene 
derivatives. 

Acetanilide, C 6 H 5 -]N1LCO.CH 3 , is readily prepared by 
boiling aniline with excess of glacial acetic acid on a reflux 
apparatus for several hours, when the aniline acetate first 
formed is slowly converted into acetanilide, with elimination 
of water. The product is purified by distillation or simply 
by recrystallisation from boiling water, 

C 6 H 5 .NH 2 , CH 3 -COOH - C 6 H 6 .NH.CO.CH 3 + H 2 0. 

It crystallises in glistening plates, melts at 112, and is 
sparingly soluble in cold, but readily in hot water; when 
heated with acids or alkalies it is rapidly hydrolysed, giving 

* Compare Part I. p. 176. 



AM I DO-COMPOUNDS J\XD AMINES. 375 

aniline and acetic acid. It is used in medicine, under the 
name of antifebrin, for reducing the temperature of the body 
in cases of fever, &c. 

Formanilide, C 6 H 5 -NH-CHO, the anilide of formic acid, 
and oxanilide, CgH^NH-CO-CO-NILC^, the anilide of 
oxalic acid, may be similarly prepared. 

Substitution Products of Aniline. Aniline and, in fact, all amido- 
compounds are much more readily attacked by halogens than are 
the hydrocarbons. When aniline, for example, is treated with 
chlorine or bromine in aqueous solution, it is at once converted 
into trichlor aniline, C 6 H 2 C1 3 -NH 2 , or tribromamline, C 6 H 2 Br 3 -NH 2 , 
so that in order to obtain mono- and di-substitution products 
indirect methods must be employed. 

The o- and p-chloranilmes, C 6 H 4 C1-NH 2 , may be prepared by 
passing chlorine into acetanilide, the ^-derivative being obtained 
in the larger quantity. The two isomerides are first separated by 
crystallisation, and then decomposed by boiling with an alkali or 
acid, 



Chloracetanilicle. Chloraniline. 

The effect of introducing an acetyl-group into the amido-group 
is therefore to render aniline less readily attacked ; acetanilide, 
in fact, behaves towards chlorine and bromine more like benzene 
than aniline. m-Chloraniline is most conveniently prepared by 
the reduction of w-chloronitrobenzene, C 6 H 4 C1'NO 2 (a substance 
formed by chlorinating nitrobenzene in the presence of antimony). 
o-Chloraniline and m-chloraniline are oils boiling at 207 and 230 
respectively, but ^-chloraniline is a solid, which melts at 70 and 
boils at 230. 

Nitranilines, C 6 H 4 (ISr0 2 )-NH 2 , cannot be obtained by nitrat- 
ing aniline, as the nitrous acid, produced by the reduction of 
the nitric acid, converts the amido- into the hydroxyl-group, 
and nitre-derivatives of phenol are formed. 

The o- and ^-compounds are prepared by nitrating acetan- 
ilide, the o- and p-nitracetanilides thus obtained being 
separated by fractional crystallisation, and then converted 
into the corresponding nitranilines by heating with alkalies. 
m-Nitraniline is very readily prepared by the partial re- 



376 AMIDO-COMPOUNDS AND AMINES. 

duction of w-dinitrobenzene, C 6 H 4 (N0 2 ) 2 , with ammonium 
sulphide (p. 369). 

o-Nitraniline melts at 71, in- at 114, andjp- at 147; they 
are all sparingly soluble in cold water, readily in alcohol, 
and on reduction they yield the corresponding o-, m-, and 
^>-pheny lenediamin es, 



Homologues of Aniline. The toluidines, or amido-toluenes, 
C 6 H 4 (CH 3 )-NH 2 , are prepared by reducing the corresponding 
o-, m-, and jp-nitrotoluenes (p. 367), by means of tin and 
hydrochloric acid, the details of the process being exactly 
similar to those already given in the case of the preparation 
of aniline from nitrobenzene, 

C ' H *<N0 3 2 + 6H = C ^X + 2H2 J 

the o- and ^-compounds may also be prepared from methyl- 
aniline (p. 370). Both o- and m-toluidine are oils boiling at 
197 and 199 respectively, but ^9-toluidine is crystalline, and 
melts at 45, boiling at 198. When treated with nitrous 
acid the toluidines yield diazo-salts, from which the corre- 
sponding cresols, C 6 H 4 (CH 3 )-OH, are obtained, and in all 
other reactions they show the greatest similarity to aniline ; 
o- and ^-toluidine are largely employed in the manufacture 
of dyes. 

Diamidobenzenes. The phenylenediaminea, C 6 H 4 (NH 2 ) 2 , are 
obtained by the reduction of the corresponding dinitrobenz- 
enes, or the nitranilines, and a general description of their 
properties has already been given (p. 373) ; o-phenylene- 
diamine melts at 102, the m- and ^-compounds at 63 and 
147 respectively. m-Phenylenediamine gives an intense 
yellow colouration with a trace of nitrous acid, and is em- 
ployed in water-analysis for the detection and estimation of 
nitrites; both the m- and ^-compounds are largely employ< 
in the manufacture of dyes. 



AMI DO-COMPOUNDS AND AMINES. 377 

Alkyl anilines. 

Those derivatives of the amido-compounds obtained "by 
displacing one or both of the hydrogen atoms of the amido- 
group by alkyl radicles are substances of considerable import- 
ance, and are usually known as alkylanilines. They are 
prepared by heating the amido-compounds, for some hours, 
with the alkyl halogen compounds, the reaction being analo- 
gous to that which occurs in the formation of secondary and 
tertiary from primary amines (p. 381), 

C 6 H 5 .NH 2 + RC1 = C 6 H 5 .NHR, HC1 
C 6 H 5 .]N T H 2 + 2EC1 = C 6 H 5 .NR 2 , HC1 + HC1. 

Instead of employing the alkyl halogen compounds, a mixture 
of the corresponding alcohol and halogen acid may be used ; 
methyl- and dimethyl-aniline, for example, are prepared, on 
the large scale, by heating aniline with methyl alcohol and 
hydrochloric acid at 200-250, 

C 6 H 5 .NH 2 , HC1 + CH 8 .OH = C 6 H 6 .NH(CH 3 ), HC1 + H 2 
C 6 H 5 .NH 2 , HC1 + 2CH 3 .OH = C 6 H 5 .N(CH 3 ) 2 , HC1 + 2H 2 0. 

These mono- and di-alkyl derivatives are stronger bases 
than the amido-compounds from which they are derived, the 
presence of the positive alkyl-group counteracting to some 
extent the action of the negative phenyl-group (compare 
p. 371) they are, in fact, very similar in properties to the 
fatty secondary and tertiary amines respectively, and may be 
regarded as derived from the fatty primary amines by the 
substitution of a phenyl-group for a hydrogen atom, just as 
the secondary and tertiary amines are obtained by displacing 
hydrogen atoms by alkyl-groups. Methylaniline, for example, 
is also phenylmethylamine, and its properties are those of a 
substitution product of methylamine. 

The mono-alkylanilines, like the secondary amines, are 
converted into yellowish nitroso-compounds on treatment 
with nitrous acid, 



378 AMIDO-COMPOUNDS AND AMINES. 

C 6 H 5 .NH-CH 3 + HO-NO - C 6 H 5 -N(NO).CH 3 + H 2 0. 

Metliylaniline. Nitrosoinethylaniline. 

(CH 3 ) 2 NH + HO-NO = (CH 8 ) 2 .N.NO + H 2 0. 

Dimetliylainine. Nitrosodiinetliylamine. 

These nitroso-com pounds give Liebermann's nitroso- reaction 

(Part I. p. 209), and on reduction they yield ammonia and the 
original alkylaniline, 

C 6 H 6 .N(NO)-CH 8 + 6H = C 6 H 5 -NH.CH 3 + NH 3 + H 2 0. 

Methylaniline, C 6 H 5 -NH-CH 3 , prepared as just described, 
is a colourless liquid which boils at 192, and, compared with 
aniline, has strongly basic properties. On adding sodium 
nitrite to its solution in hydrochloric acid, nitrosomethyl- 
aniline, C 6 H 5 .N(NO)-CH 3 , separates as a light-yellow oil. 

Dimethylaniline, C 6 H 5 -N(CH 3 ) 2 , the preparation of which 
has just been given, is a colourless, strongly basic oil, which 
boils at 192 ; it is largely used in the manufacture of dyes. 

The di-alkylanilines, such as dimethylaniline, C 6 H 5 -N(CH 3 ) 2 , also 
interact readily with nitrous acid (a behaviour which is not shown 
by tertiary fatty amines), intensely green (iso)nitroso-com pounds 
being formed, the NO- group displacing hydrogen of the nucleus 
from the ^-position to the nitrogen atom, 



Nitrosodimethylaniline. 

These substances do not give Liebermann's nitroso-reaction, and 
when reduced they yield derivatives of ^-phenylenediamine, 



Dimethyl-p-phenyleneclitiniine. 
p-Nitrosodimethijlamline, C 6 H 4 <Cxr/nTT \ > * s prepared by dis- 



solving dimethylaniline (1 part) in water (5 parts), and concen- 
trated hydrochloric acid (2-5 parts), and gradually adding to the 
well-cooled solution the calculated quantity of sodium nitrite, 
dissolved in a little water. The yellow crystalline precipitate of 
nitrosodimethylaniline hydrochloride is separated by filtration, 
dissolved in water, decomposed by potassium carbonate, and the 
free base extracted with ether. Nitrosodimethylaniline crystal- 



AMIDO-COMPOUNDS AND AMINES. 379 

lises from ether in dark-green plates, and melts at 85 ; it is not 
a nitrosamine, because the NO- group is not united to nitrogen, 
and does not give Liebermann's nitroso-reaction. When reduced 
with zinc and hydrochloric acid it is converted into dimethyl-p- 
phetiylenediamine (see above), and when boiled with dilute soda 
it is decomposed into dimethylamine and p-nitrosophenol or quinone 
monoxime (compare p. 426), 



Diphenylamine and Triplienylamine. 

The hydrogen atoms of the amido-group in aniline may 
also be displaced by phenyl radicles, the compounds diphenyl- 
amine, (C 6 H 5 ) 2 NH, and triphenylamine, (C 6 H 5 ) 3 N, being pro- 
duced. These substances, however, cannot be obtained by 
treating aniline with chlorobenzene, C 6 H 5 C1, a method which 
would be analogous to that which is employed in the prepara- 
tion of diethylamine and triethylamine, because the halogen 
is so firmly bound to the nucleus that no action takes place 
even when the substances are heated together. 

Diphenylamine is most conveniently prepared by heating 
aniline hydrochloride with aniline at about 240 in closed 
vessels, 

C 6 H 6 .NH 2 , HC1 + C 6 H 6 .NH 2 = (C 6 H 5 ) 2 -NH + JS T H 4 C1. 

It is a crystalline substance, melts at 54, boils at 310, 
and is insoluble in water. It is only a feeble base, and its 
salts are decomposed by water ; its solution in concentrated 
sulphuric acid gives with a trace of nitric acid an intense 
blue colouration, and it therefore serves as a very delicate test 
for nitric acid or nitrates. Diphenylamine is largely used in 
the manufacture of dyes, also for experiments in which a 
high constant temperature is required, as, for example, in 
determining the vapour density of substances of high boiling- 
point by Y. Meyer's method. When treated with potassium, 
diphenylamine yields a solid potassium derivative, (C 6 H 5 ) 2 NK, 
the presence of the two phenyl-groups being sufficient to 



380 AMIDO-COMPOUNDS AND AMINES. 

impart to the >NH group a feeble acid character, similar 
to that of imides (Part I. p. 243). 

Triphenylamine, (C 6 H 5 ) 3 N, may be prepared by heating 
potassium diphenylamine with bromobenzene at 300, 

(C 6 H 5 ) 2 NK + C 6 H 6 Br - (C 6 H 6 ) 8 N + KBr. 
It is a colourless, crystalline substance, melts at 127, and 
does not combine with acids. 

Aromatic Amines. 

The true aromatic amines namely, those compounds in 
which the amido-group is united with carbon of the side-chain 
are of far less importance than the amido-compounds, and, as 
will be seen from the following example, they closely resemble 
the fatty amines in chemical properties. 

Benzylamine, C 6 H 5 -CH 2 -NH 2 , may be obtained by reducing 
phenyl cyanide (benzonitrile, p. 433) or benzaldoxime (p. 419), 

C 6 H 5 -CN + 4H = C 6 H 6 .CH 2 .NH 2 
C 6 H B -CH:NOH + 4H = C 6 H 5 -CH 2 .NH 2 + H 2 0, 
by treating the amide of phenylacetic acid (p. 442) with 
bromine and potash, 

C 6 H 5 .CH 2 .CO-NH 2 + Br + 4KOH = 

C 6 H 5 -CH 2 .NH 2 + 2KBr + K 2 C0 3 + 2H 2 0, 

and by heating benzyl chloride with alcoholic ammonia, 

C 6 H 5 -CH 2 C1 + NH 3 = C 6 H 6 .CH 2 .NH 2> HC1. 
All these methods are similar to those employed in the 
preparation of fatty primary amines (Part I. pp. 211-212). 

Benzylamine is a colourless, pungent-smelling liquid, boiling 
at 187; it closely resembles the fatty amines in nearly all 
respects, and differs from the monamido-compounds (aniline, 
toluidine, &c.) in being strongly basic, alkaline to litmus, and 
readily soluble in water. Like the fatty primary amines, 
it gives the carbylamine reaction, and when solutions of its 
salts are treated with nitrous acid it is converted into the 



AMIDO COMPOUNDS AND AMINES. 381 

corresponding alcohol (benzyl alcohol, p. 415), and not into a 
diazo-compound. 

Secondary and tertiary aromatic amines are formed when a 
primary amine is heated with an aromatic halogen compound, 
containing the halogen in the side-chain; when, for example, 
henzylamine is heated with henzyl chloride, hoth dibenzylamine 
and tribenzylamine are produced, just as diethylamine and triethyl- 
amine are obtained when ethylamine is heated with ethyl bromide, 

C 6 H 5 .CH -NH 2 + C 6 H 5 .CH 2 C1 = (C 6 H 5 .CH 2 ) 2 NH, HC1 
C 6 H 5 .CH 2 .NH 2 + 2C 6 H 5 .CH 2 C1 = (C 6 H 5 .CH 2 ) 3 N, HC1 + HC1. 
When, therefore, benzyl chloride is heated with ammonia, the 
product consists of a mixture of the salts of all three amines. 



CHAPTER XXY. 

DIAZO-COMPOUNDS AND THEIR DERIVATIVES. 

It has already been stated that when the amido-compounds 
or their salts are treated with nitrous acid in warm aqueous 
solution, they yield phenols; if, however, a well-cooled, 
dilute solution of aniline hydrochloride (1 mol.) be mixed 
with sodium nitrite (1 mol.), and hydrochloric acid (1 mol.) 
added to set free the nitrous acid, phenol is not produced, 
and the solution contains an unstable substance called diazo- 
benzene chloride, the formation of which may be expressed 
by the equation, 

C 6 H 5 .NH 2 ,HC1 + N0 2 H - C 6 H 5 .N 2 C1 + 2H 2 0. 

In this respect, then, the amido-compounds differ from the 
fatty amines ; the latter are at once converted into alcohols 
by nitrous acid in the cold, whereas the former are first 
transformed into diazo-compounds, which, usually only on 
warming, decompose more or less readily with formation of 
phenols (p. 398). 

All amido-compounds (that is to say, compounds in which 
the -NH 2 group is directly united with the benzene nucleus) 



382 DIAZO-COMPOUNDS AND THEIR DERIVATIVES. 

behave in this way, and yield diazo-salts similar to diazo- 
benzene chloride in constitution. 

The diazo-salts were discovered in 1860 by P. Griess, and 
may be regarded as salts of diazobenzene, C 6 H 5 -N 2 -OH, and 
its derivatives. 

The bases or hydroxides from which these salts are derived have 
not yet been isolated, as when liberated from their compounds they 
immediately change into highly explosive, very unstable products 
which seem to be their anhydrides. 

The diazo-salts (usually spoken of as the diazo-compounds) 
may be isolated without much difficulty, although, as a matter 
of fact, they are seldom separated from their aqueous solutions, 
partly because of their highly explosive character, but princi- 
pally because for most purposes for which they are prepared 
this operation is quite unnecessary. 

Preparation. Diazo-salts may be obtained in crystals by 
treating a well-cooled solution of an amido-com pound in 
absolute alcohol with amyl nitrite and a mineral acid, as far 
as possible in absence of water,* 
C 6 H 5 .NH 2 ,HC1 + C B H n -O.NO = 

C 6 H 6 -N 2 C1 + C 5 H n .OH + H 2 0. 

Diazobenzene sulphate, C 6 H 5 .N 2 'SO 4 H, for example, is prepared by 
dissolving aniline (15 parts) in absolute alcohol (10 parts), adding 
concentrated sulphuric acid (20 parts), and after cooling in a 
freezing mixture, slowly running in pure amyl nitrite (20 grams) ; 
after 10-15 minutes diazobenzene sulphate separates in crystals, 
which are washed with alcohol and ether, and dried in the air at 
ordinary temperatures. 

Diazobenzene chloride and diazobenzene nitrate may be obtained 
in a similar manner, employing alcoholic solutions of hydrogen 
chloride and of nitric acid in the place of sulphuric acid. 

Diazobenzene nitrate, C 6 H 5 -N 2 -NO 3 , may also be conveniently 
isolated as follows : Aniline nitrate is suspended in a small quantity 
of water, and the liquid saturated with nitrous acid (generated 
from As 4 6 and HN0 3 ), when the crystals gradually dissolve with 

* Amyl nitrite is used instead of sodium nitrite because it is soluble 
in alcohol. 



PIAZO-COMPOUNDS AND THEIR DERIVATIVES. 383 

formation of diazobenzene nitrate ; on the addition of alcohol 
and ether, this salt separates in colourless needles. Special pre- 
cautions are to be observed in preparing this substance, as when 
dry it is highly explosive, although it may be handled with com- 
parative safety if kept moist. 

Solutions of the diazo-salts are prepared by dissolving the 
anrido-compound in an aqueous mineral acid, and adding the 
proper quantity of a solution of sodium nitrite, the tempera- 
ture being kept at or below ; examples are given later 
(pp. 384-385). 

Properties. The diazo-salts are colourless, crystalline com- 
pounds, very readily soluble in water ; in the dry state they 
are more or less explosive, and should be handled only 
with the greatest caution. They are of immense value in 
synthetical chemistry and in the preparation of dyes, as they 
undergo a number of remarkable reactions, of which the 
following are some of the more important. 

When heated with (absolute) alcohol they yield hydro- 
carbons, part of the alcohol being oxidised to aldehyde, 

C 6 H 5 .N 2 C1 + C 2 H 5 -OH = C 6 H 6 + N 2 + HC1 + CH 3 - CHO. 

When warmed in aqueous solution they decompose rapidly, 
with evolution of nitrogen and formation of phenols (p. 398), 

C 6 H 5 .N 2 .S0 4 H + H 9 - C 6 H 5 .OH + N 2 + H 2 S0 4 
C 6 H 4 (CH 3 ).N 2 C1 + H 2 = C 6 H 4 (CH 8 ).OH + N 2 + HC1, 

2>-Diazotoltiene Chloride. ^-Cresol. 

but if warmed with concentrated halogen acids they give 
halogen derivatives, 

C H 5 .N 2 .S0 4 H + HI = C 6 H 5 I + N 2 + H 2 S0 4 ; 

this last reaction is made use of principally for the prepara- 
tion of iodo-derivatives (p. 358), because when the other 
halogen acids are used, the product contains the correspond- 
ing phenol. 

The diazo-compounds behave in a very remarkable way 
when treated with cuprous salts j if, for example, a solution 
of diazobenzene chloride be warmed with cuprous chloride, 



384 DIAZO-COMPOUNDS AND THEIR DERIVATIVES. 

nitrogen is evolved, but instead of phenol, chlorobenzene is 
produced. In this reaction the diazo-salt combines with 
the cuprous chloride to form a brownish additive compound, 
which is decomposed at higher temperatures, cuprous chloride 
being regenerated; theoretically, therefore, the reaction is 
continuous, 

C 6 H 5 .N 2 C1, 2CuCl = C 6 H 5 C1 + N 2 + 2CuCl. 

If, instead of the chloride, cuprous bromide or cuprous 
iodide be employed, bromobenzene or iodobenzene is produced, 

C 6 H 6 -N a Cl, 2CuBr = C 6 H 5 Br + N 2 + CuCl + CuBr, 

Additive Compound. Bromobenzene. 

whereas by using cuprous cyanide, a cyanide or nitrile is 
formed (compare p. 434), 

C 6 H 5 .N 2 C1, 2CuCJST - C 6 H 5 -CN + N 2 + CuCl + CuCK 

Additive Compound. Phenyl Cyanide. 

By means of these very important reactions, which were 
discovered by Sandmeyer in 1884, it is possible to displace 
the NH 2 - group in amido-compounds by Cl, Br, I, CN, and 
indirectly by COOH (by the hydrolysis of the CN- group), 
and indeed by other atoms or groups ; as, moreover, the yield 
is generally good, Sandmeyer's reaction is of great practical 
value. The amido-compounds being readily obtainable from 
the nitro-compounds, and the latter from the hydrocarbons, 
this method affords a means of preparing halogen, cyanogen, 
and other derivatives indirectly from the hydrocarbons. 

It will be seen from the above statements that the preparation 
of a halogen, cyanogen, or other derivative from the amido-com- 
pountl involves two distinct reactions : firstly, the preparation of a 
solution of the diazo-salt ; and secondly, the decomposition of this 
salt in the most suitable manner. 

As an example of the method employed in preparing a solution 
of the diazo-salt, the following m.iy serve: Aniline (1 part) is dis- 
solved in a mixture of ordinary concentrated hydrochloric acid 
(about 2 parts) and water (about 2| parts), and the solution is 
cooled by the addition of coarsely powdered ice ; when the tempera- 
ture has fallen to about 5 an aqueous solution of the theoretical 



DIAZO-COMPOUNDS AND THEIR DERIVATIVES. 385 

quantity of sodium nitrite * is slowly run in from a tap-funnel, 
stirring constantly and keeping the temperature as low as possible. 
The solution now contains diazobenzene chloride ; if sulphuric had 
been used instead of hydrochloric acid, diazobenzene sulphate would 
have been formed. The aniline is said to be diazotised. 

If, now, the solution of the diazo-salt be warmed alone, nitrogen 
is evolved and phenol is produced ; if, however, it be slowly added 
to a hot solution of cuprous chloride, chlorobenzene is produced, 
whereas by using cuprous cyanide, cyanobenzene is formed (p. 434). 
In all these cases the final product is usually separated by distilla- 
tion in steam (compare also p. 358). 

Gattermann has shown that in many cases the decomposition 
of the diazo-compounds is best brought about by adding copper 
powder (prepared by the action of zinc-dust on a solution of 
copper sulphate) to the cold acid solution of the diazo-salt ; when, 
for example, a solution of diazobenzene chloride is treated in this 
way, nitrogen is evolved and chlorobenzene produced, the reaction 
being complete in about half-an-hour. 

The diazo-compounds also serve for the preparation of an 

important class of compounds known as the liydrazines, these 

substances being obtained by reducing the diazo-compounds, 

usually with stannous chloride and hydrochloric acid (p. 388), 

R-N 2 C1 + 4H = R.NH.NH 2 ,HC1. 

Diazochloride. Hydrazine Hydrochloride. 

Constitution of Diazo-compounds. The state of combina- 
tion of the two nitrogen atoms and of the acid radicle in 
diazo-salts has formed the subject of much discussion, and 
until recently the view first expressed by Kekule (1866), that 
diazo-salts have the constitution C 6 H 5 -N:NR (where R = C1, 
Br, I, N0 3 , HS0 4 , &c.), was generally adopted. That only 
one of the two nitrogen atoms is directly united to the 
nucleus is clearly shown by many facts as, for example, by 
the conversion of the diazo-salts into rawzo-halogen deriva- 
tives, monohjdric phenols, &c., and by their conversion into 
hydrazines, such as C 6 H 5 -NH-NH 2 , on reduction (p. 388). 

* As commercial sodium nitrite is often highly impure and the quantity 
to be used cannot be determined by weighing, a considerable excess is dis- 
solved and the solution is run in until the solution of the diazo-salt contains 
free nitrous acid (as shown by starch-potassium-iodide paper) after stirring 
well and leaving for a short time. 

Org. Chetn. Y 



386 DIAZO-COMPOUNDS AND THEIR DERIVATIVES. 

That the acid radicle is combined with the nitrogen atom 
which is not directly united to the nucleus seems to be 
proved by many reactions of diazo-salts as, for example, 
the following : Diazobenzene chloride interacts readily with 
dimethylaniline, giving dimethylamidoazobenzene (p. 388), 



C 6 H 5 .N:N.C 6 H 4 .N(CH 3 ) 2 .+ HC1, 

a b 

and this substance, on reduction, yields aniline and dimethyl- 
>-phenylenediamine (p. 388), 
C 6 H 6 .N:N.C fl H 4 .N(CH 8 ) 2 + 4H = 



a b 

These changes are easily explained on the assumption that 
the acid radicle is attached to the ^-nitrogen atom, as in the 
above formula, but apparently they could not very well take 
place if the acid radicle were united to the a-nitrogen atom, 
as in the formula C 6 H 5 -NC1:N, suggested by Bloomstrand. 

a b 

There is, however, one fact which seems to point to the formula 
C 6 H 5 -NR:N, namely, that the physical properties of dilute solutions 
of the diazo-salts are similar to those of solutions of quaternary 
ammonium salts, such as C 6 H 5 -NR=(CH 3 ) 3 , in which the acid 
radicle is directly united to pentavalent nitrogen. Probably, there- 
fore, the two formulae C 6 H 5 -N:NR and C 6 H 5 -NR:N represent 
tautomeric forms (Part I. p. 200), and the diazo-salts interact in 
one or the other form according to the conditions of the experiment ; 
for these reasons the diazo-group may be conveniently represent 
by -N 2 -, as in most of the formulae used above, without indicating 
the actual state of combination of the two nitrogen atoms. 

Diazoamido- and Amidoazo-compounds. 

Although some of the more characteristic reactions of 
diazo-com pounds have already been mentioned, there are 
numerous other changes of great interest and of great com- 
mercial importance which these substances undergo. 

When, for example, diazobenzene chloride is treated with 
aniline, a reaction takes place similar to that which occurs 



DIAZO-COM POUNDS AND THEIH DERIVATIVES. 387 

when benzoyl chloride is treated with aniline (p. 432), and 
diazoamidobenzene is formed, 



6 H 5 = C 6 H 6 .N 2 .NH.C 6 H 5 + HC1 

Diazoamidobenzene. 

C 6 H 5 -COC1 + NH 2 -C 6 H 5 m C 6 H 5 .CO-NH.C 6 H 5 + HC1. 

Benzoylainidoberizene or Benzanilide. 

As, moreover, other diazo-compounds and other amido- 
compounds interact in a similar manner, numerous diazoamido- 
compounds may be obtained. 

Diazoamidobenzene, C 6 II 5 -N 2 -NILC 6 H 5 , may be described 
as a typical compound of this class ; it is conveniently pre- 
pared by passing nitrous fumes into an alcoholic solution of 
aniline, the diazobenzene hydroxide, which is probably first 
produced, interacting with excess of aniline, 

C 6 H 5 -N 2 .OH + C 6 H 5 .NH 2 = C 6 H 6 .N 2 .NH.C 6 H 5 + H 2 0. 

Diazoamidobenzene crystallises in brilliant yellow needles, 
and is sparingly soluble in water, but readily in alcohol and 
ether ; it is very feebly basic, and forms only very unstable 
salts with acids. 

Amidoazobenzene, C 6 H 5 -N 2 -C 6 H 4 -NH 2 , is formed when 
diazoamidobenzene is warmed with a small quantity of aniline 
hydrochloride at 40, intramolecular change taking place, 

C 6 H 6 .N 2 -NH.C 6 H 5 = C 6 H 5 -N 2 .C 6 H 4 .NH 2 . 

This remarkable reaction, which is a general one and shown by 
all diazoamido-compounds, may be compared with that which 
occurs in the transformation of methylaniline into paratoluidine 
(p. 370), the group -N 2 -C 6 H 5 leaving the nitrogen atom and 
migrating to the joam-position in the nucleus, 

C 6 H 5 .NH-N 2 -C 6 H 5 C 6 H 4 <N 2 H c 6 H 5 

Diazoamidobenzene. p- Amidoazobenzene. 

C 6 H 5 .NH-CH 3 C 6 H 4 <^ 3 

Methylaniline. p-Toluidine. 

That the group -N 2 C 6 H 5 displaces hydrogen from the j0-position to 
the -NH 2 group is proved by the fact that the amicloazobenzene 



388 DIAZO-COMPOUNDS AND THEIR DERIVATIVES. 

thus produced is converted into jra-phenylenediamine and aniline 
on reduction with tin and hydrochloric acid, 



Amidoazobenzene may also be prepared by nitrating 
azobenzene (p. 391), and then reducing with ammonium 
sulphide the p-nitroazobenzene, C 6 H 5 -N 2 -C 6 H 4 -N0 2 , which is 
thus produced ; these changes are analogous to those which 
occur in the formation of aniline from benzene and the 
formation of amidoazobenzene in this way proves that it is 
an amido-derivative of azobenzene. 

Amidoazobenzene crystallises from alcohol in brilliant 
orange-red plates, and melts at 123; its salts are intensely 
coloured, the hydrochloride, C 6 H 5 .N 2 -C 6 H 4 .NH 2 , HC1, for 
example, forms beautiful steel-blue needles, and used to come 
into the market under the name of ' aniline yellow ' as a silk 
dye (p. 535). 

Other amidoazo-compounds may be obtained directly by treating 
tertiary alkylanilines (p. 377) with diazo-salts : dimethylaniline, for 
example, interacts with diazobenzene chloride, yielding dimethyl- 
amidoazobenzene, 

C 6 H 5 -N 2 C1 + C 6 H 5 .N(CH 3 ) 2 - C 6 H 5 .N 2 .C 6 H 4 .N(CH 3 ) 2 , HC1, 
no intermediate diazoamido- compound being formed, because 
dimethylaniline does not contain an NH< or NH 2 - group. 

In this case also the diazo-group, C 6 H 5 -N 2 -, takes up the 
^-position to the N(CH 3 ) 2 - group, as is shown by the fact that, 
on reduction, dimethylamidoazobenzene is converted into aniline 
and dimethyl-j9-phenylenediamine, the latter being identical with 
the base which is produced by reducing jt?-nitrosodimethylaniline 
(p. 378). 

Phenylhydrazine, C 6 H 5 -NH-NH 2 , a compound of great 
practical importance, is easily prepared by the reduction of 
diazobenzene chloride, 

HCL 



Aniline (1 part) is dissolved in concentrated hydrochloric acid 
(20 parts), and diazotised in the usual way (p. 384) ; the solution 
of diazobenzene chloride is then mixed with stannous chloride 
(45 grams) dissolved in concentrated hydrochloric acid (45 grams). 



DIAZO-COMPOUNDS AND THEIR DERIVATIVES. 389 

The precipitate of phenylhydrazine hydrochloride, which rapidly 
forms, is separated by filtration, dissolved in water, decomposed 
Avith potash, and the free base extracted with ether and purilied 
by distillation, preferably under reduced pressure. 

Phenylhydrazine crystallises in colourless prisms, melts at 
23, and boils at 241, decomposing slightly. It is sparingly 
soluble in cold water, readily in alcohol and ether ; it is a 
strong base, and forms well-characterised salts, such as the 
hydrochloride, C 6 H 5 -NH-NH 2 , HC1, which crystallises in 
colourless needles, and is readily soluble in hot water; 
solutions of the free base and of its salts reduce Fehling's 
solution in the cold. The constitution of phenylhydrazine is 
established by the fact that, when heated with zinc-dust and 
hydrochloric acid, it is converted into aniline and ammonia. 

Phenylhydrazine interacts readily with aldehydes, ketones, 
and most substances containing a carbonyl- group, with 
elimination of water and formation of phenylhydrazones 
(hydrazones) ; as these compounds are usually sparingly 
soluble and often crystallise well, they may frequently be 
employed with advantage in the identification and isolation 
of aldehydes and ketones (Part I. p. 136), 



Benzaldehyde. Benzylidene Hydrazone. 



Acetophenone. Acetophenone Hydrazone. 

Many hydrazones are decomposed by strong mineral acids, 
ith regeneration of the aldehyde or ketone, and formation of 
salt of phenylhydrazine, 

3 6 H 6 .CH:N.NH-C 6 H 6 + H 2 + HC1 = 

C 6 H 5 .CHO + C 6 H 5 .KH-NH 2 , HC1; 

m reduction with zinc-dust and acetic acid they yield primary 
imines, 



6 H 5 + 4H = C,H 5 -CH 2 .NH 2 + C 6 H 6 -NH 2 . 

Benzylidenehydrazone. Benzylamine. 



390 DIAZO-COMPOUNDS AND THEIR DERIVATIVES. 

The value of phenylhydrazine as a means of detecting and. 
isolating the sugars has already been explained (Part I. p. 272). 

In preparing hydrazones, the reacting substances may either be 
heated together without a solvent, or more frequently the sub- 
stance is dissolved in water (or alcohol), and the solution of the 
requisite amount of phenylhydrazine in dilute acetic acid added. 
On warming, the hydrazone frequently separates in a crystalline 
form, and may be readily purified by recrystallisation. 

Osazones (Part I. p. 273) are prepared by boiling an aqueous 
solution of a sugar with excess of phenylhydrazine acetate ; after 
some time the osazone begins to be deposited in a crystalline form, 
the separation increasing as the liquid cools. 

Azo- and Azoxy '-compounds. 

It has already been stated that when mtro-compoimds 
are treated with tin and hydrochloric acid, and other acid 
reducing agents, they are converted into amido-compounds, 
a similar change taking place when alcoholic ammonium 
sulphide is employed; when, however, nitro-compounds are 
treated with other alkaline reducing agents, such as alcoholic 
potash, sodium amalgam and water, stannous oxide and soda, 
or zinc-dust and soda, they yield azo-co?npounds, such as 
azobenzene azoxy-compounds, such as azoxybenzene, being 
formed as intermediate products ; in these reactions two 
molecules of the nitro-com pound afford one molecule of the 
azoxy- or azo-compound, 



2C 6 H 6 .NO a + 6H = C 6 H 5 .N<.>N-C 6 H 5 + 3H 2 

Azoxy benzene. 

2C 6 H 5 .N0 2 + 8H = C fl H 6 .N:N.C 6 H 6 + 4H 2 0. 

Azobenzene. 

Azoxybenzene, C 6 H 5 -N<C _ >N-C 6 H 5 , is generally pre- 
pared by adding nitrobenzene (1J parts) to a solution of 
sodium (1 part) in methyl alcohol and then boiling (reflux 
condenser) for about four hours ; after distilling the alcohol, 
water is added, and when sufficiently hard the pasty product 
is pressed on porous earthenware, left to dry, and crystallised 



DIAZOCOMPOUNDS AND THEIR DERIVATIVES. 391 

from light petroleum. It forms yellow needles melting at 
36, and is insoluble in water, but readily soluble in most 
organic liquids. 

Azobenzene, CgHg-NiN-CgH^ may be prepared by mixing 
azoxybenzene (1 part) with iron filings (3 parts) and dis- 
tilling carefully from a small retort; the solid distillate is 
purified as described in the case of the azoxy-compound. 
Azobenzene crystallises in brilliant red plates, melts at 68, 
and distils at 293 ; it is readily soluble in ether and alcohol, 
but insoluble in water. Alkaline reducing agents, such as 
ammonium sulphide, zinc-dust and soda, &c., convert azoben- 
zene into hydrazobenzene, a colourless, crystalline substance, 
which melts at 131, 

C 6 H 5 .N:N.C 6 H 5 + 2H = C 6 H 5 .NH.NH-C 6 H 5 , 
whereas a mixture of zinc-dust and acetic acid decomposes it, 
with formation of aniline, 

C 6 H 6 .N:N.C 6 H 6 + 4H = 2C 6 H 5 -NH 2 . 
Other azo-compounds behave in a similar manner. 

Hydrazobenzene, C 6 H 5 -NH-NH-C 6 H 5 , is readily converted 
into azobenzene by mild oxidising agents such as mercuric 
oxide, and slowly even when air is passed through its alco- 
holic solution. When treated with strong acids it undergoes 
a very remarkable intramolecular change, and is converted 
into ^-diamidodiphenyl or benzidine, a strongly basic sub- 
stance largely used in the preparation of azo-dyes (p. 537), 



Hydrazobenzene. Beuzidine. 

Benzidine maybe produced in one operation by reducing azobenzene 
with tin and strong hydrochloric acid. Other azo-compounds behave 
in a similar manner; orthoazo-toluene, CH 3 -C 6 H 4 -N:N-C 6 H 4 -CH 3 , 
for example, is first converted into the corresponding hydrazo-com- 
pound, which then undergoes isomeric or intramolecular change 
into dimethylbenzidine (tolidine), 



<2>CH 3 __... 

These changes, like that of diazoarnidobenzene into ^-amidoazo- 



DlAZO-COMPOUNDS AND THEIR DERIVATIVES. 

benzene (p. 387), involve the migration of a complex group of atoms 
from an amido-group to the para -position in the nucleus, 

1 "tT 

C 6 H 5 .NH-NH.C 6 H 5 - 

if the jo-position be already occupied, isomeric change takes place 
far less readily, and the group migrates to the or^Ao-position. 



CHAPTER XXVI. 

SULPHONIC ACIDS AND THEIR DERIVATIVES. 

When benzene is heated with concentrated sulphuric acid 
it gradually dissolves, and benzenesulphonic acid is formed by 
the substitution of the sulplionic group -S0 3 H or -S0 2 -OH 
for an atom of hydrogen, 

C 6 H 6 + H 2 S0 4 = C 6 H 6 .SO S H + H 2 0. 

The homologues of benzene and aromatic compounds in 
general behave in a similar manner, and this property of 
readily yielding sulphonic derivatives by the displacement of 
hydrogen of the nucleus is one of the important characteristics 
of aromatic, as distinct from fatty, compounds. 

The sulphonic acids are not analogous to the alkylsulphuric 
acids (Part I. p. 185), which are esters, but rather to the 
carboxylic acids, since they may be regarded as derived from 
sulphuric acid, S0 2 (OH) 2 , just as the carboxylic acids are de- 
rived from carbonic acid, CO(OH) 2 , namely, by the substitu- 
tion of an aromatic radicle for one of the hydroxyl-groups. 



Sulphuric acid, SO^r: Carbonic acid, 
U-tl 

T> 

Sulphonic acid, S0 2 < OTT Carboxylic acid, 
Preparation. Sulphonic acids are prepared by treating an 



SULPHONIC ACIDS AND THEIR DERIVATIVES. 393 

aromatic compound with sulphuric acid, or with anhydrosul- 
phuric acid, 

pTT 

C 6 H 5 .CH 3 + H 2 S0 4 = C 6 H 4 < 3 + H 2 



C 6 H 5 -NH 2 + H 2 S0 4 = C 6 H 4 < 2 H + H 2 

C 6 H 6 + 2H 2 S0 4 = C 6 H 4 (S0 3 H) 2 + 2H 2 0. . 
The number of hydrogen atoms displaced by sulphonic 
groups depends (as in the case of nitro-groups) on the 
temperature, on the concentration of the acid, and on the 
nature of the substance undergoing sulplionation. 

The substance to be sulphonated is mixed with, or dissolved in, 
excess of the acid, and, if necessary, the mixture or solution is then 
heated on a water- or sand-bath until the desired change is com- 
plete. After cooling, the product is carefully poured into water, 
and the acid isolated as described later (p. 395). In the case of a 
substance which is insoluble in water or dilute sulphuric acid, the 
point at which the whole is converted into a monosulphonic acid is 
easily ascertained by taking out a small portion of the mixture and 
adding water ; unless the whole is soluble, unchanged substance is 
still present. 

Sometimes chlorosulphonic acid, C1-SO 3 H, is employed in sul- 
phonating substances, and in such cases chloroform or carbon 
disulphide may be used as a solvent to moderate the action, 
C 6 H 6 + C1.SO 8 H = C 6 H 5 .S0 3 H + HC1. 

Properties. Sulphonic acids are, as a rule, crystalline, 
readily soluble in water, and often very hygroscopic ; they 
have seldom a definite melting-point, and gradually decom- 
pose when heated, so that they cannot be distilled. They 
have a sour taste, a strongly acid reaction, and show, in fact, 
all the properties of powerful acids, their basicity depending 
on the number of sulphonic groups in the molecule. They 
decompose carbonates, and dissolve certain metals with evolu- 
tion of hydrogen ; their metallic salts (including the barium 
salts), as a rule, are readily soluble in water. 

Although, generally speaking, the sulphonic acids are very 
stable, and are not decomposed by boiling aqueous alkalies or 



394 SULPHONIC ACIDS AND THEIR DERIVATIVES. 

mineral acids, they undergo certain changes of great import- 
ance. When fused with potash they yield phenols (p. 398), 
and when strongly heated with potassium cyanide, or with 
potassium ferrocyanide, they are converted into cyanides 
(or nitriles, p. 434), which distil off, leaving a residue of 
potassium sulphite, 

C 6 H 5 -S0 3 K + KCN = C 6 H 5 -CN + K 2 S0 8 . 

The sulphonic group may also be displaced by hydrogen. 
This may be done by strongly heating the acids alone, or with 
hydrochloric acid in sealed tubes, or by passing superheated 
steam into the acids, or into their solution in concentrated 
sulphuric acid. 

Sulphonic acids yield numerous derivatives, which may 
generally be prepared by methods similar to those used in 
the case of the corresponding derivatives of carboxylic acids. 
When, for example, a sulphonic acid (or its alkali salt) is 
treated with phosphorus pentachloride, the hydroxyl-group 
is displaced by chlorine, and a sulphonic chloride is obtained, 

C 6 H 5 .S0 2 -OH + PC1 5 = C 6 H 5 .S0 2 C1 + POC1 3 + HC1. 

All sulphonic acids behave in this way, and their sulphonic 
chlorides are of great value, not only because they are often 
useful in isolating and identifying the ill-characterised acids, 
but also because, like the chlorides of the carboxylic acids, 
they interact readily with many other compounds. 

The sulphonic chlorides are decomposed by water am 
by alkalies, giving the sulphonic acids or their salts ; the;) 
interact with alcohols at high temperatures, yielding etheree 
salts, such as ethyl benzene.sulphonate, 

C 6 H 5 .S0 2 C1 + C 2 H 5 .OH = C 6 H 5 .S0 2 .OC 2 H 5 + HC1, 

and when shaken with concentrated ammonia they are usualb 
converted into well-defined crystalline sulphonamides, whicl 
also serve for the identification of the acids, 



C 6 H 5 .S0 2 C1 + NH 3 = C 6 H 5 -S0 2 .NH 2 + HC1. 

Beiizenesulpliouic Chloride. Benzeiiesulphonamide. 



SULPHONIC ACIDS AND THEIR DERIVATIVES. 395 

The isolation of sulphonic acids is very often a matter of some 
difficulty, because they are readily soluble in water and non- 
volatile, and cannot be extracted from their aqueous solutions 
by shaking with ether, &c., or separated from other substances 
by steam distillation. The first step usually consists in separat- 
ing them from the excess of sulphuric acid employed in their 
preparation ; this may be done in the following manner : The 
aqueous solution of the product of sulphonation (see above) is 
boiled with excess of barium (or calcium) carbonate, filtered from 
the precipitated barium (or calcium) sulphate, and the filtrate 
which contains the barium (or calcium) salt of the sulphonic acid 
treated with sulphuric acid drop by drop as long as a precipitate is 
produced ; after again filtering, an aqueous solution of the sulphonic 
acid is obtained, and on evaporating to dryness, the acid remains 
as a syrup or in a crystalline form. If calcium carbonate lias 
been used, the acid will contain a little calcium sulphate, which 
may be got rid of by adding a little alcohol, filtering, and again 
evaporating. 

Lead carbonate is sometimes employed instead of barium or 
calcium carbonate ; in such cases the filtrate from the lead sul- 
phate is treated with hydrogen sulphide, filtered from lead sulphide, 
and then evaporated. These methods are, of course, only appli- 
cable provided that the barium, calcium, or lead salt of the acid 
be soluble in water; in other cases the separation is much more 
troublesome. 

When two or more sulphonic acids are present in the product, 
they are usually separated by fractional crystallisation of their 
salts ; the alkali salts are easily prepared from the barium, 
calcium, or lead salts by treating the solution of the latter with 
the alkali carbonate as long as a precipitate is produced, filtering 
from the insoluble carbonate, and then evaporating. 

Sometimes a complete separation cannot be accomplished with 
the aid of any of the salts, and in such cases the sulphonic chlorides 
are prepared by treating the alkali salts with phosphorus penta- 
chloride ; these compounds are soluble in ether, chloroform, &c., 
and generally crystallise well, so that they are easily separated and 
obtained in a state of purity. 

Benzenesulphonic acid, C 6 H 5 -SO ;3 H, is prepared by gently 
boiling a mixture of equal volumes of benzene and con- 
centrated sulphuric acid for twenty to thirty hours, using 
a reflux condenser ; it is isolated with the aid of its barium 
or lead salt, both of which are soluble in water. It 



396 SULPHONIC ACIDS AND THEIR DERIVATIVES. 

crystallises with 1| mols. H 2 in colourless, hygroscopic 
plates, and dissolves freely in alcohol; when fused with 
potash it yields phenol (p. 404). BenzenesulpJionic chloride, 
C 6 H 5 -S0 2 C1, is an oil, but the sulphonamide, C 6 H 5 -S0 2 -NH 2 , 
is crystalline, and melts at 150. 

Benzene-ra-disulphonic acid, C 6 H 4 (S0 3 H) 2 , is also pre- 
pared by heating the hydrocarbon with concentrated sulphuric 
acid, but a larger proportion (two volumes) of the acid is 
employed, and the solution is heated more strongly (or 
anhydrosulphuric acid is used) ; when fused with potash, it 
yields resorcinol (p. 411). 

The three (o.m.p.) toluenesulphonic acids, C 6 H 4 (CH 3 )-S0 3 H, 
are crystalline, and their barium salts are soluble in water ; 
only the o- and p-acids are formed when toluene is dissolved 
in anhydrosulphuric acid. 

Sulphanilic acid, amidobenzene-^-sulphonic acid, or aniline- 
jp-sulphonic acid, C 6 H 4 (NH 2 )-S0 3 H, is easily prepared by 
heating aniline sulphate at about 200 for some time. 

A'niline is slowly added to a slight excess of the theoretical 
quantity of sulphuric acid contained in a porcelain dish, the 
mixture being constantly stirred as it becomes solid ; the dish is 
then gently heated on a sand-bath, the contents being stirred, and 
care being taken to prevent charring. The process is at an end 
as soon as a small portion of the product, dissolved in water, gives 
no oily precipitate of aniline on adding excess of soda. After 
cooling, a little water is added, and the sparingly soluble sulphonic 
acid separated by filtration, and. purified by recrystallisation from 
boiling water, with addition of animal charcoal if necessary. 

Sulphanilic acid crystallises with 2 mols. H 2 0, and is 
readily soluble in hot, but only sparingly in cold, water. 
It forms salts with bases, but it does not combine with 
acids, the basic character of the amido-group being neutral- 
ised by the acid character of the sulphonic group ; in this 
respect, therefore, it differs from glycine (Part I. p. 299), 
which forms salts both with acids and bases. 

When sulphanilic acid is dissolved in dilute soda, the 
solution mixed with a slight excess of sodium nitrite, and 



SULPHONIC ACIDS AND THEIR DERIVATIVES. 397 

poured into well-cooled, dilute sulphuric acid, diazobenzene-p- 
sulphonic acid is formed, 



O = C 

this compound, however, immediately loses water, and is con- 

N 
verted into its anhydride,* C 6 H 4 < Q 2 >, which separates 

3 

from the solution in colourless crystals. 

Diazobenzenesulphonic acid, or rather its anhydride, shows 
the characteristic properties of diazo-compounds in general ; 
when boiled with water it is converted into phenol->-sul- 
phonic acid (p. 408), 
N" 



whereas when heated with concentrated hydrochloric or 
hydrobromic acid it gives chlorobenzene- or bromobenzene-j^- 
sulphonic acid, 



it interacts readily with dimethylaniline, giving helianthin 
(p. 536). 

Amidobenzene-o-sulphonic acid and the w-acid (metanilic acid) 
may be obtained by reducing the corresponding nitrobenzene- 
sulphonic acids, C 6 H 4 (NO 2 )-SO 3 H, both of which are formed, to- 
gether Avith the ^?-acid, on nitratipg benzenesulphonic acid ; they 
resemble sulphanilic acid in properties, and are readily converted 
into the anhydrides of the corresponding diazobenzenesulphonic 
acids. 

Many other sulphonic acids are described later. 

* The existence of this anhydride (and of that of amidobenzene-m- 
sulphonic acid) is a very interesting fact because, as a rule, anhydride 
formation takes place only between groups in the o-position to one 
another (compare p. 437). 



398 PHENOLS. 



CHAPTER XXVII. 

PHENOLS. 

The hydroxy-compounds of the aromatic series, such as 
phenol or hydroxy-benzene, C 6 H 5 -OH, the isomeric hydroxy- 
toluenes, C 6 H 4 (CH 3 )-OH, and benzyl alcohol, C 6 H 5 -CH 2 .OH, 
are derived from the aromatic hydrocarbons by the sub- 
stitution of hydroxyl-groups for atoms of hydrogen, just as 
the fatty alcohols are derived from the paraffins. It will be 
seen, however, from the examples just given that whereas, 
in benzene, hydrogen atoms of the nucleus must necessarily 
be displaced, in the case of toluene and all the higher 
homologues this is not so, since the hydroxyl-groups may 
displace hydrogen either of the nucleus or of the side- 
chain. Now the hydroxy-derivatives of benzene, and all 
those aromatic hydroxy-compounds formed by the substitu- 
tion of hydroxyl-groups for hydrogen atoms of the nucleus, 
differ in many respects not only from the fatty alcohols, 
but also from those aromatic compounds which contain the 
hydroxyl-group in the side-chain; it is convenient, there- 
fore, to make some distinction between the two kinds of 
aromatic hydroxy-compounds, and for this reason they are 
classed in two groups, (a) the phenols, and (b) the aromatic 
alcohols (p. 414). 

The phenols, then, are hydroxy-compounds in which the 
hydroxyl-groups are united directly with carbon of the 
nucleus ; they may be subdivided into monohydric, dihydric, 
trihydric phenols, &c., according to the number of hydroxyl- 
groups which they contain. Phenol, or carbolic acid, 
C 6 H 5 -OH, for example, is a monohydric phenol, as are also 
the three isomeric cresols or hydroxytoluenes, C 6 H 4 (CH 3 )-OH ; 
the three isomeric dihydroxy benzenes, C 6 H 4 (OH) 2 , on the 






PHENOLS. 399 

other hand, are dihydric phenols, whereas phloroglucinol, 
C 6 H 3 (OH) 3 , is an example of a trihydric compound. 

Many of the phenols are easily obtainable, well-known 
compounds ; carbolic acid, for instance, is prepared from 
coal-tar in large quantities ; carvacrol and thymol occur in 
various plants ; and catechol, pyrogallol, &c. may be obtained 
by the dry distillation of certain vegetable products. 

Preparation. Phenols may be prepared by treating salts 
of amido-compounds with nitrous acid in aqueous solution, 
and then heating until nitrogen ceases to be evolved, 

C 6 H 5 .NH 2 ,HC1 + HO-NO = C 6 H 5 -OH + N 2 + H 2 + HC1 



, HC1 + HO-NO = CH< + ^2 + H 2 + HC1. 



It is possible, therefore, to prepare phenols not only from 
the amido-compounds themselves, but also indirectly from 
the corresponding nitro-derivatives and from the hydro- 
carbons, since these substances may be converted into amido- 
compounds, 

C 6 H 6 C 6 H 5 .N0 2 C 6 H 5 -NH 2 C 6 H 5 -OH. 

Benzene. Nitrobenzene. Amidobenzene. Phenol. 

The conversion of an amido-com pound into a phenol really 
takes place in two stages, as already explained (p. 381); at 
ordinary temperatures the salt of the amido-compound is 
transformed into a salt of a diazo-compound, but on heating 
its aqueous solution the latter decomposes, yielding a phenol, 

C 6 H 5 -NH 9 , HC1 + HC1 + KN0 2 = C 6 H 5 .N C1 + KC1 + 2H 2 
C 6 H 5 .N 2 C1 + H 2 = C 6 H 5 .OH + HOI + N 2 . 

The amido - compound, aniline, for example, is dissolved in 
dilute hydrochloric acid or sulphuric acid, and diazotised in the 
manner already described (p. 384). The solution of the diazo-salt 
is then gradually heated to boiling (reflux condenser), until the 
evolution of nitrogen (which at first causes brisk effervescence) is at 
an end ; the phenol is afterwards separated from the tarry matter, 
which is almost invariably produced, l>y distillation in steam, by 
crystallisation from hot water, or by extraction with ether ; in the 
last case the ethereal solution is usually shaken with dilute caustic 



400 PHENOLS. 

soda, which dissolves out the phenol, leaving most of the impurities 
in the ether. 

Dihydric phenols may sometimes be prepared from the 
corresponding di-substitution products of the hydrocarbon, as 
indicated by the following series of changes, 



. 
C 6 H 6 C 6 H 4 < 

Benzene. Dinitrobenzene. Diamidobenzeue. Diazo-salt. Dihydric Phenol. 

They may also be obtained from the monohydric compounds 
in the following manner, 

C 6 H 5 -OH C 6 H 4 2 2 



Phenol. Nitrophenol. Amidophenol. Diazo-salt. Dihydric Phenol. 

These two methods, however, are limited in their application, 
because o- and w-diamido-compounds cannot always be converted 
into the corresponding diazo-salts, but more often yield products of 
quite a different nature ; o- and jt?-amido-hydroxy-compounds also 
show an abnormal behaviour with nitrous acid, the former not 
being acted on at all, the latter only with difficulty. For these 
reasons dihydric phenols are usually most conveniently prepared by 
the methods given later. 

Another important general method of preparing phenols 
consists in fusing sulphonic acids or their salts with potash 
or soda ; in this case, also, their preparation from the hydro- 
carbons is often easily accomplished, since the latter are 
usually converted into sulphonic acids without difficulty, 
C 6 H 5 -S0 3 K + KOH = C 6 H 5 .OH* + K 2 S0 3 

C ^ < so 3 k + NaOH = C ^< on 3 + Na * s 3- 

The sulphonic acid or its alkali salt is placed in an iron or, 
better, nickel or silver dish,t together with excess of solid potash 
(or soda) and a little water, and the dish is heated over a free 
flame, the mixture being constantly stirred with a nickel or silver 
spatula, or with a thermometer, the bulb of which is encased in a 

* In all cases the phenols are present in the product as alkali salts. 
f Caustic alkalies readily attack platinum and porcelain at high tempera- 
tures, but have little action on nickel and none on silver. 



PHENOLS. 401 

glass tube, or covered with a film of silver ; * after the potash 
and the salt have dissolved, the temperature is slowly raised, 
during which process the mixture sometimes undergoes a variety 
of changes in colour, by which an experienced operator can tell 
when the decomposition of the sulphonic acid is complete ; as 
a rule, a temperature considerably above 200 is required, so 
that simply boiling the sulphonic acid with concentrated potash 
does not bring about the desired change. When the operation 
is finished the fused mass is allowed to cool, dissolved in water, 
the solution acidified with dilute sulphuric acid, and the liberated 
phenol isolated in some suitable manner (p. 399). 

Dihydric phenols may often be obtained in a similar 
manner from the disulphonic acids, 

C 6 H 4 (S0 3 K) 2 + 2KOH = C 6 H 4 (OH) 2 + 2K 2 S0 3 . 
Owing to the high temperature at which these reactions must 
be carried out, secondary changes very often occur. When 
the sulphonic acid contains halogen atoms, the latter are 
usually displaced by hydroxyl-groups, especially if other acid 
radicles, such as -N0 2 or -S0 3 H, be also present ; when, 
for example, chlorobenzenesulphonic acid, C 6 H 4 C1-S0 3 H, is 
fused with potash, a dihydric phenol, C 6 H 4 (OH) 2 , is produced, 
the halogen as well as the sulphonic group being eliminated. 
For this reason also, compounds such as o- and ^>-chloro- 
nitrobenzene may be converted into the corresponding nitro- 
phenols (p. 405), even by boiling them with concentrated 
potash, the presence of the nitro-group facilitating the dis- 
placement of the halogen atom ; m-chloronitrobenzene, on 
the other hand, is not acted on under these conditions. Some- 
times also the process is not one of direct substitution only 
that is to say, the hydroxyl-groups in the product are not 
united with the same carbon atoms as those with which the 
displaced atoms or groups were united ; the three (o.m.p.) 
bromobenzenesulphonic acids, for example, all yield one and 
the same dihydric phenol namely, the m-compound, resor- 
cinol, C 6 H 4 (OH) 2 , because the o- and j>-dihydric compounds, 

* As the mixture is very liable to spirt, the eyes of the operator must be 
protected by spectacles or by a sheet of glass placed suitably before him, 
Org. Chem. Z 



402 PHENOLS. 

which are first produced from the corresponding bromo- 
sulphonic acids, are converted into the more stable ra-deriva- 
tive by intramolecular change. 

There are several less important methods by which phenols may 
be obtained, as, for example, by distilling hydroxy-acids, such as 
salicylic acid, with lime, 

C 6 H 4 (OH) -COOH = C 6 H 5 .OH + CO 2 , 

a reaction which is similar to that which occurs in preparing the 
hydrocarbons from the acids. 

Also by heating other phenols with fatty alcohols in presence 
of zinc chloride, when the alkyl-group displaces hydrogen of the 
nucleus, just as in the production of toluidine, &c., from aniline 
(P. 370), 

C 6 H 5 .OH + C 2 H 5 .OH = C 6 H 4 < 2 5 + H 2 O. 



Properties. Most phenols are colourless, crystalline sub- 
stances, readily soluble in alcohol and ether ; their solubility 
in water usually increases with the number of hydroxyl- 
groups in the molecule, phenol and cresol, for example, 
being sparingly soluble, whereas the three dihydric phenols 
and the trihydric compounds are readily soluble. Conversely, 
their volatility diminishes ; so that although phenol and cresol 
distil without decomposing, and are readily volatile in steam, 
the trihydric phenols usually undergo decomposition, and 
volatilise very slowly in steam. Alcoholic and aqueous 
solutions of phenols (and of some of their carboxylic acids) 
give a green, violet, or yellow colouration with ferric salts, 
the particular colouration depending, in the case of the 
di- and poly-hydric compounds, on the relative positions of 
the hyclroxyl-groups. 

o-Dihydroxy-compounds give an intense green colouration, 
which first becomes deep violet and then bright red 01 
addition of sodium bicarbonate ; m-dihydroxy-compounds gii 
a deep violet colouration ; ^?-dihydroxy-compounds give 
faint green colouration, which immediately changes to yellow 
owing to the formation of a quinone (p. 425). 

All phenols give Liebermann's reaction ; when dissolved ii 



PHENOLS. 403 

concentrated sulphuric acid and treated with a nitroso-com- 
pound or a nitrite, they yield coloured solutions, which, after 
diluting and adding excess of alkali, assume an intense blue 
or green colour. This reaction, therefore, affords a convenient 
test for phenols as well as for nitroso-compounds (Part I. 
p. 209). 

Although phenols resemble the fatty alcohols and the 
alcohols of the aromatic series in some respects, they have, 
on the whole, very little in common with these substances. 
The reason of this is, that the character of the hydroxyl-group 
(like that of the amido-group, p. 371) is greatly modified by 
its union with carbon of the benzene nucleus, just as that of 
the hydroxyl-group in water is altered by combination with 
acid-forming atoms or radicles such as C1-, N0 2 -, &c., as, 
for example, in HOC1 and HON0 2 ; in other words, the 
phenolic hydroxyl-group has a much more pronounced acid 
character than that in alcohols, the radicles phenyl, C 6 H 5 -, 
phenylene, C 6 H 4 <, &c., being therefore regarded as acid- 
forming. 

The acid character of the hydroxyl-group in phenols is shown 
in their behaviour with caustic alkalies, in which they dissolve 
freely, forming metallic derivatives or salts, such as sodium 
phenate, C 6 H 5 -ONa, and potassium cresate, C 6 H 4 (CH 3 )-OK; 
these compounds, unlike the alkali derivatives of the alcohols, 
are stable in presence of water, but are decomposed by carbon 
dioxide and by all other acids, with regeneration of the 
phenols. For this reason phenols which are insoluble in 
water are insoluble in alkali carbonates, unless they contain 
other acid-forming groups or atoms, as, for example, in nitro- 
phenol, C 6 H 4 (M) 2 ).OH, and picric acid, C 6 H 2 (N0 2 ) 3 .OH, 
when their acid character is often enhanced to such an extent 
that they decompose and dissolve in alkali carbonates. 

The metallic derivatives of the phenols, like those of the 
alcohols, interact with alkyl halogen compounds and with 
acid chlorides, yielding substances analogous to the ethers 
and esters respectively, 



404 PHENOLS. 



C 6 H 5 -OK + CH 3 I = C 6 H 5 .O.CH 3 + KI 



C 6 H 4< OK 3 + CH 3 -COC1 = C 6 H 4 < C 3 0>C 

the former, like the ethers, are not decomposed by boiling 
alkalies, but the latter undergo hydrolysis, just as do the 
esters, 

C.H t <Jg W j H . + KOH = C 6 H 4 <| 3 + C 2 H 3 2 K. 

Towards pentachloride and pentabromide of phosphorus, 
and towards acetic anhydride and acetyl chloride, phenols 
behave in the same way as the alcohols, 

C 6 H 5 -OH + PC1 5 = C 6 H 5 C1 + POC1 3 + HC1 * 
C 6 H 5 .OH + (CH 3 .CO) 2 = C 6 H 5 .O.CO-CH 3 + C 2 H 4 2 . 
When heated with acids, however, the phenols are not 
changed to any appreciable extent, because, being less basic 
in character than the alcohols, they do not so readily form 
salts. 

The constitution of a phenol being quite different from 
that of a primary or secondary alcohol, the fact that they do 
not yield aldehydes or ketones on oxidation was only to be 
expected ; they are, however, somewhat similar in constitu- 
tion to the tertiary alcohols, and, like the latter, they often 
undergo complex changes on oxidation. 

Monohydric Phenols. 

Phenol, carbolic acid, or hydroxybenzene, C 6 H 5 -OH, occurs 
in very small quantities in human urine and also in that 
of cows ; it may be obtained from benzene, nitrobenzene, 
aniline, diazobenzene chloride, benzenesulphonic acid, and 
salicylic acid (p. 450) by the methods already given, but the 
whole of the phenol of commerce is prepared from coal-tar 

* Compare foot-note, Part I. p. 92. 



PHENOLS. 405 

(compare p. 307), in which it was discovered by Kunge 
in 1834. 

Phenol crystallises in colourless, deliquescent prisms, which 
melt at 42 and turn pink on exposure to air and light ; it 
boils at 183, and is volatile in steam. It has a very character- 
istic smell, is highly poisonous, and has a strong caustic action 
on the skin, quickly causing blisters. It dissolves freely in 
most organic liquids, but is only sparingly soluble (1 part in 
about 15) in cold water; its aqueous solution gives a violet 
colouration with ferric chloride, and a pale-yellow precipitate 
of tribromophenol, C 6 H 2 Br 3 -OH (in. p. 92), with bromine 
water ; both these reactions may serve for the detection of 
phenol. Owing to its poisonous and antiseptic properties, 
phenol is extensively used as a disinfectant ; it is also em- 
ployed in large quantities for the manufacture of picric acid. 
Potassium phenate, C 6 H 5 -OK, is obtained when phenol is 
dissolved in potash and the solution evaporated ; it is a 
crystalline substance, readily soluble in water, and is decom- 
posed by carbon dioxide with separation of phenol. 

Phenyl methyl ether, or anisole, C 6 H 5 -0-CH 3 , may be pre- 
pared by heating potassium phenate with methyl iodide ; it is 
a colourless liquid, boiling at 155, and is similar to the ethers 
of the fatty series in chemical properties, although it also 
shows the usual behaviour of aromatic compounds, and readily 
yields nitro-derivatives, &c. When warmed with concen- 
trated hydriodic acid it yields phenol and methyl iodide, 

C 6 H 5 .0-CH 3 + HI = C 6 H 5 .OH + CH 8 L 

Phenyl ethyl ether, or phenetole, C 6 H 5 -0-C 2 H 5 , can be 
>btained in a similar manner; it boils at 172. 
Nitrophenols, C 6 H 4 (N0 2 )-OH, are formed very readily on 
mating phenol even with dilute .nitric acid, the presence of 
hydroxyl-group not only facilitating the introduction of 
le nitro-group, but also determining the position taken up 
by the latter. When phenol is gradually added to nitric acid 
of sp. gr. 1-11 (6 parts), the mixture being kept cold and 



406 PHENOLS. 

frequently shaken, it is converted into ortho- and >ara-nitro- 
phenol, which separate as a dark-brown oil or resinous mass. 

This product is allowed to settle, washed with water by decanta- 
tion, and then submitted to distillation in steam, whereupon the 
or^Ao-nitrophenol passes over as a yellow oil, which crystallises on 
cooling ; the solution in the flask is heated to boiling, and filtered 
from tarry matter, the jmra-iiitrophenol which separates on cooling 
being purified by recrystallisation from boiling water with addition 
of animal charcoal. 

Meta-nitropUenol is prepared by reducing meta-dinitroben- 
zene to meta-nitraniline (p. 375), and treating a solution of 
the latter in excess of dilute sulphuric acid with nitrous acid ; 
the solution of the diazo-salt is then slowly heated to boiling, 
and the meta-nitrophenol thus produced purified by recrystal- 
lisation from water. 

The melting-points of the three compounds are : 

Ortho-nitrophenol, Meta-nitrophenol, Para-nitrophenol, 

45. 96. 114. 

The o- and the m-compounds are yellow, but the p-derivative 
is colourless ; only the o-compound is volatile in steam. The 
three compounds are all sparingly soluble in cold water, but 
dissolve freely in alkalies and also in alkali carbonates, form- 
ing dark-yellow or red salts which are not decomposed by 
carbon dioxide ; they have, therefore, a more marked acid 
character than phenol itself, the presence of the nitro-group 
having an effect comparable to that of the nitro-group in 
nitric acid, H0-N0 2 . 

Picric acid, or trinitrophenol, C 6 H 2 (lSr0 2 ) 3 -OH, is formed 
when substances such as wool, silk, leather, and resins are 
heated with concentrated nitric acid, very complex reactions 
taking place ; it may be obtained by heating phenol, or the 
o- and >-nitro phenols, with nitric acid, but the product is 
not very easily purified from resinous substances which 
are formed at the same time. 

Picric acid is best prepared by dissolving phenol (1 part) in 
an equal weight of concentrated sulphuric acid, and adding this 



PHENOLS. 407 

solution to nitric acid of sp. gr. 1-4 (3 parts) in small quantities at 
a time ; after the first energetic action has subsided, the mixture 
is carefully heated on a water-bath for about two hours. On cool- 
ing, the product solidifies to a mass of crystals, which are collected, 
washed, and recrystallised from hot water. 

When phenol is dissolved in sulphuric acid it is converted into 
a mixture of o- and ^-phenolsulphonic acids, C 6 H 4 (OH)-SO 3 H (see 
below) ; on subsequent treatment with nitric acid, the sulphonic 
group, as well as two atoms of hydrogen, are displaced by nitro- 
groups, 

C 6 H 4 <^ H + 3HO.N0 2 = C 6 H 2 (N0 2 ) 3 .OH + H 2 S0 4 + 2H 2 O. 

Picric acid is a yellow crystalline compound, melting at 
122-5. It is only very sparingly soluble in cold, but moder- 
ately easily in hot, water, and its solutions dye silk and wool 
(not cotton, p. 514) a beautiful yellow colour; it is, in fact, 
one of the earliest known artificial organic dyes. It has very 
marked acid properties, and readily decomposes carbonates. 
The potassium derivative, C 6 H 2 (N0 2 ) 3 -OK, and the sodium 
derivative, C 6 H 2 (N0 2 ) 3 -ONa, are yellow crystalline com- 
pounds, the former being sparingly, the latter readily, soluble 
in cold water. These compounds, and also the ammonium 
derivative, explode violently on percussion or when heated, 
and are employed in the preparation of explosives; picric 
acid itself burns quietly when ignited, but can be caused to 
explode violently with a detonator. 

Picric acid may be produced by oxidising l:3:5-trinitrobenzene, 
C 6 H 3 (NO 2 ) 3 , with potassium ferricyanide, the presence of the nitro- 
groups facilitating the substitution of hydroxyl for hydrogen ; as, 
moreover, it is quite immaterial which of the three hydrogen 
atoms is displaced, since they all occupy a similar position rela- 
tively to the rest of the molecule, the constitution of picric acid 
must be represented by the formula, 

OH 




NO, 



408 PHENOLS. 

Picric acid has the curious property of forming crystalline com- 
pounds with benzene, naphthalene, anthracene, and many other 
hydrocarbons, so that it is sometimes used in detecting and also in 
purifying small quantities of the substances in question ; the com- 
pound which it forms with benzene, for example, crystallises in 
yellow needles, is decomposed by water, and has the composition 
C 6 H 2 (N0 2 ) 3 .OH, C 6 H 6 . 

PJienol-o-sulpJionic acid, C 6 H 4 (OH)-S0 3 H, is formed, to- 
gether with a comparatively small quantity of the ^>-acid, 
when a solution of phenol in concentrated sulphuric acid is 
kept for some time at ordinary temperatures ; if, however, 
the solution be heated at 100-110, the o-acid, which is the 
primary product, is gradually converted into phenol-p-sulphonic 
acid. 

Phenol-m-sulphonic acid is prepared by carefully heating 
benzene-m-disulphonic acid with potash at 170-180; under 
these conditions only one of the sulphonic groups is displaced, 

e\O TT- OT^ 

C 6 H 4 <gQ J + 2KOH = C 6 H 4 <^ K + K 2 S0 3 + H 2 0. 

The o-acid is interesting on account of the fact that it is 
converted into the p-acid when boiled with water, and also 
because it is used as an antiseptic under the name aseptol. 

The three (am.>.) cresolsorhydroxytoluenes,C 6 H 4 (CH 3 )-OH, 
the next homologues of phenol, occur in coal-tar, but cannot 
be conveniently isolated from this source owing to the 
difficulty of separating them from one another; they are 
prepared from the corresponding toluidines or amidotoluenes, 
C 6 H 4 (CH 3 )-NH 2 , by means of the diazo-reaction, or by fusing 
the corresponding toluenesulphonic acids with potash, 

C 6 H 4 < + KOH = C 6 H 4 < + K 2 S0 3 . 



They resemble phenol in most ordinary properties, as, for 
example, in being sparingly soluble in water, and in forming 
potassium and sodium derivatives, which are decomposed by 
carbon dioxide ; they also yield alkyl-derivatives, &c., by the 



PHENOLS. 409 

displacement of the hydrogen of the hydroxyl-group. On 
distillation with zinc-dust they are all converted into toluene, 



and they all give a bluish colouration with ferric chloride. 

One very curious fact regarding the three cresols is that 
they are not oxidised by chromic acid, although toluene, 
as already stated, is slowly converted into benzoic acid ; 
the presence of the hydroxyl-group, therefore, protects the 
methyl-group from the attack of acid oxidising agents, and 
this is true also in the case of other phenols of similar 
constitution. If, however, the hydrogen of the hydroxyl- 
group be displaced by an alkyl, or by an acid group such as 
acetyl, then the protection is withdrawn, and the methyl- 
group is converted into the carboxyl-group in the usual 
manner ; the methylcresols, C 6 H 4 (OCH 3 )-CH 3 , for example, 
are oxidised by chromic acid, yielding the corresponding 
methoxybenzoic acids, C 6 H 4 (OCH 3 )'COOH. 

The melting and boiling points of the three cresols are 
given below. 

Ortho-cresol. Meta-cresol. Para-cresol. 

M.p. 31 5 36 

B.p. 188 201 198 

Of the higher monohydric phenols, thymol and carvacrol 
may be mentioned ; these two compounds are isomeric mono- 
hydroxy-derivatives of cymene, C 6 H 4 (CH 3 )-C 3 H 7 (p. 349), and 
their constitutions are respectively represented by the formulae, 

CH 3 CH 3 

fT" 

' LJ 

CH(CH 3 > 2 CH(CH 3 > 2 . 

Thymol. Carvacrol. 

Thymol occurs in oil of thyme, together with cymene ; it 
crystallises in large plates, melts at 51-5, and has a charac- 




410 PHENOLS. 

teristic smell like that of thyme. It is only very sparingly 
soluble in water, and does not give a colouration with ferric 
chloride ; when heated with phosphoric anhydride it yields 
propylene and m-cresol, 

C 6 H,(OH)<^ = C 6 H 4 (OH)-CH 3 + C 3 H 6 . 

Carvacrol occurs in the oil of Origanum hirtum, and is 
easily prepared by heating camphor with iodine, 

CioH 16 + 1 2 = C 10 H 14 + 2HI ; 

it is an oil boiling at 237, and its alcoholic solution gives a 
green colouration with ferric chloride. When heated with 
phosphoric anhydride, it is decomposed into propylene and 
o-cresol. 

Dihydric Phenols. 

The isomeric dihydric phenols catechol, resorcinol, and 
hydroquinone are well-known compounds of considerable 
importance, and are respectively represented by the formulae, 

OH OH OH 

^ I I 

-OH 



Catechol Resorcinol Hydroquinone 

(Ortho-dihydroxybenzene). (Meta-dihydroxybenzene). (Para-dihydroxybenzeue). 

Catechol, or pyrocatechol, C 6 H 4 (OH) 9 , occurs in catechu, 
a substance obtained in India from Acacia catechu and other 
trees, and was first obtained by the dry distillation of this 
vegetable product ; it may be obtained by fusing phenol-o- 
sulphonic acid, C 6 H 4 (OH)-S0 3 H, with potash, but is most 
conveniently prepared by heating guaiacol or methylcatechol, 
a solid (m.p. 28) contained in the tar of beechwood, with 
concentrated hydriodic acid, 






+ HI = C 6 H 4 < + CH 3 I 



PHENOLS. 411 

It is a colourless, crystalline substance, melting at 104, and 
is readily soluble in water ; its aqueous solution gives, with 
ferric chloride, a green colouration, which, on the addition of 
sodium bicarbonate, changes first to violet and then to red, a 
reaction which is common to all or^o-dihydric phenols (p. 402). 
Guaiacol shows a similar behaviour with ferric chloride, but 
when the hydrogen atoms of both the hydroxyl-groups are 
displaced, as, for example, in dimethylcatechol or veratrol, 
C 6 H 4 (OCH 3 ) 2 , there is no colouration. 

Resorcinol, C 6 H 4 (OH) 2 , is prepared on a large scale by 
fusing benzene-m-disulphonic acid with potash, 

C 6 H 4 <g J + 2KOH = C 6 H 4 <JJ + 2K 2 S0 3> 

but it is also obtained when the para-disulphonic acid, and 
many other ortho- and para-derivatives of benzene are treated 
in the same way, owing to intramolecular change taking place 
(compare p. 401). It is a crystalline substance, melting at 
110, and dissolves freely in water, alcohol, and ether; its 
aqueous solution gives a dark-violet colouration, with ferric 
chloride and a crystalline precipitate of tribromoresorcinol, 
C 6 HBr 3 (OH) 2 , with bromine water. When resorcinol is 
strongly heated for a few minutes with phthalic anhydride 
(p. 439), and the brown or red mass is then dissolved in 
soda, there results a brownish-red solution, which when 
poured into a large volume of water shows a beautiful green 
fluorescence; this phenomenon is due to the formation of 
fluoresce'in (p. 532). Other ra-dihydric phenols give this 
fluorescein reaction, which, therefore, affords a convenient 
and very delicate test for such compounds; the fluorescein 
reaction may also be employed as a test for anhydrides of 
certain dicarboxylic acids (p. 437). 

Resorcinol is used in large quantities in preparing fluorescein, 
eosin, and various azo-dyes. 

Hydroquinone, or quinol, C 6 H 4 (OH) 2 , is formed, together 
with glucose, when the glucoside, arbutin a substance 



412 PHENOLS. 

which occurs in the leaves of the bear-berry is boiled 
with water, 

C 12 H 16 7 + H 2 = C 6 H 4 (OH) 2 + C 6 H 12 6 . 

It is usually prepared by reducing quinone (p. 425) with 
sulphurous acid in aqueous solution, and then extracting with 
ether, 

C 6 H 4 2 + H 2 S0 3 + H 2 = C 6 H 4 (OH) 2 + H 2 S0 4 . 

It melts at 169, is readily soluble in water, and when treated 
with ferric chloride or other mild oxidising agents it is con- 
verted into quinone, 

C 6 H 4 (OH) 2 + = C 6 H 4 2 + H 2 0. 

Trihydric Phenols. 

The three trihydric phenols, C 6 H 3 (OH) 3 , which should 
exist in accordance with theory, are all known, and are 
respectively represented by the following formulae, 



-OH I \ * ^~ C 

-OH HO L J OH 



Pyrogallol. Plilordglucinol. Hydroxyhydroquinone. 

1:2: 3-Trihydroxybenzene. 1:3: 5-Triliydroxy benzene. 1:2: 4-Trihydroxybenzene. 

Pyrogallol, C 6 H 3 (OH) 3 , sometimes called pyrogallic acid, is 
prepared by heating gallic acid (p. 452) alone or with glycerol, 
at about 210, until the evolution of carbon dioxide ceases, 

C 6 H 2 (OH) 3 .COOH = C 6 H 3 (OH) 3 + C0 2 . 

It is a colourless, crystalline substance, melting at 115, 
and is readily soluble in water, but more sparingly in 
alcohol and ether (the effect of hydroxyl-groups) ; its aqueous 
solution gives, with ferric chloride, a red, and with ferrous 
sulphate containing a trace of ferric chloride, a deep, dark- 
blue colouration. It dissolves freely in alkalies, giving 






PHENOLS. 413 

solutions which rapidly absorb oxygen and turn black 
on exposure to the air, a fact which is made use of in 
gas analysis for the estimation of oxygen. Pyrogallol has 
powerful reducing properties, and precipitates gold, silver, 
and mercury from solutions of their salts, being itself 
oxidised to oxalic and acetic acids; many other phenols, 
such as catechol, resorcinol, and hydroquinone, show a similar 
behaviour, especially in alkaline solution, but the monohydric- 
compounds are much less readily oxidised, and consequently 
do not exhibit reducing properties. Pyrogallol and hydro- 
quinone are used in photography as developers. 

Like glycerol and other trihydric-compounds, pyrogallol 
forms mono-, di-, and tri-alkyl-derivatives, as, for example, 
C 6 H 3 (OH) 2 .OC 2 H 5 , C 6 H 3 (OH)(OC 2 H 5 ) 2 , and C 6 H 3 (OC 2 H 5 ) 3 ; 
the dimethyl-deiiv&tive, C 6 H 3 (OCH 3 ) 2 -OH, occurs in beech- 
wood tar. 

Phloroglucinol, 1:3:5-, or symmetrical trihydroxybenzene, 
C 6 H 3 (OH) 3 , is produced when phenol, resorcinol, and many 
resinous substances, such as gamboge, dragon's-blood, &c. } are 
fused with potash. 

It is best prepared by fusing resorcinol (1 part) with soda 
(6 parts) for about twenty-five minutes, or until the vigorous 
evolution of hydrogen has ceased ; the chocolate-coloured melt 
is dissolved in water, acidified with sulphuric acid, extracted 
with ether, the ethereal extract evaporated, and the residue 
recrystallised from water. 

It crystallises with 2 mols. H 2 in colourless prisms, melts 
at about 218, and is very soluble in water; the solution, 
which has a sweet taste, gives, with ferric chloride, a bluish- 
violet colouration, and when mixed with potash it rapidly 
turns brown in contact with air owing to absorption of 
oxygen. When digested with acetyl chloride, phloroglucinol 
yields a triacetate, C 6 H 3 (C 2 H 3 2 ) 3 , melting at 106, and in 
many other reactions its behaviour points to the conclusion 
that it contains three hydroxyl-groups ; on the other hand, 
when treated with hydroxylamine it gives a trioxime, 



414 PHENOLS. 

C 6 H 6 (N-OH) 3 , and in this and certain other respects it 
behaves as though it were a triltetone. 

For these reasons phloroglucinol may be represented by 
one of the following formulae, 
OH 





and it may be assumed that the trihydroxy-compound is 
readily convertible into the triketone and vice versd by 
tautomeric change (compare Part I. p. 200). 

Hydroxyhydroquinone, or l:2:4-trihydroxybenzene, is formed 
when hydroquinone is fused with potash. It melts at 140, is very 
soluble in water, and its aqueous solution is coloured greenish- 
brown by ferric chloride, but on the addition of sodium bicarbonate 
the colour changes to blue and then to red (p. 402). 



CHAPTER XXVIII. 

AROMATIC ALCOHOLS, ALDEHYDES, KETONES, AND QUINONES. 

Alcohols. 

The aromatic alcohols are derived from the hydrocarbons by 
substituting hydroxyl-groups for hydrogen atoms of the side- 
chain : benzyl alcohol, C 6 H 5 .CH 2 -OH, for example, is derived 
from toluene; tolyl alcohol, C 6 H 4 (CH 3 )-CH 2 .OH, from xylene; 
and so on. The compounds of this kind are very closely 
related to the alcohols of the fatty series, although, of course, 
they show at the same time the general behaviour of aromatic 
substances. 

They may be prepared by methods exactly analogous to 
those employed in the case of the aliphatic alcohols namely, 



AROMATIC ALCOHOLS, ALDEHYDES, ETC. 415 

by heating the corresponding halogen derivatives with water, 
weak alkalies, or silver hydroxide, 

C 6 H 5 .CH 2 C1 + H 2 = C 6 H 5 .CH 2 .OH + HC1, 
and by reducing the corresponding aldehydes and ketones, 

C 6 H 5 .CHO + 2H = C 6 H 5 .CH 2 .OH 
C 6 H 5 -CO-CH 3 + 2H = C 6 H 5 -CH(OH).CH 3 . 
Those compounds which, like benzyl alcohol, contain the 
carbinol group, -CH 2 -OH, directly united, with the benzene 
nucleus, may also be prepared by treating the corresponding 
aldehydes with potash (compare p. 420), 

2C 6 H 5 .CHO + KOH = C 6 H 5 .CH 2 -OH + C 6 H 5 -COOK. 
The aromatic alcohols are usually colourless liquids or 
solids, sparingly soluble in water ; their behaviour with alkali 
metals, phosphorus pentachloride, and acids is similar to that 
of the fatty compounds, as will be seen from a consideration 
of the properties of benzyl alcohol, one of the few well-known 
aromatic alcohols. 

Benzyl alcohol, or phenylcarbinol, C 6 H 5 -CH 2 -OH, an 
isomeride of the three cresols (p. 408), occurs in storax (a 
resin obtained from the tree, Styrax officinalis\ and also in 
balsam of Peru and balsam of Tolu, either in the free state or 
as an ester in combination with cinnamic or benzole acid. 

It may be obtained by reducing benzaldehyde (p. 418) with 
sodium amalgam, 

C 6 H 5 .CHO + 2H = C 6 H 5 .CH 2 .OH, 

and by boiling benzyl chloride with a solution of sodium 
carbonate, 

C 6 H 5 .CH 2 C1 + H 2 = C 6 H 5 -CH 2 .OH + HC1 ; 
but it is most conveniently prepared by treating benzaldehyde 
with cold potash, 

2CJL.CHO + KOH = C fi H,-CH 9 .OH + OJ 



The aldehyde (10 parts) is shaken with a solution of potash 
(9 parts) in water (10 parts) until the whole forms an emulsion, 
which is then allowed to stand for twenty-four hours ; after adding 



416 AROMATIC ALCOHOLS, ALDEHYDES, 

water to dissolve the potassium benzoate, the solution is extracted 
with ether, the dried ethereal extract evaporated, and the benzyl 
alcohol purified by distillation. 

Benzyl alcohol is a colourless liquid, boiling at 206 ; it is 
only sparingly soluble in water, but miscible with alcohol, 
ether, &c., in all proportions. It dissolves sodium and 
potassium with evolution of hydrogen, yielding metallic 
derivatives which are decomposed by water, and when 
treated with phosphorus pentachloride it is converted into 
benzyl chloride, 

C 6 H 5 .CH 2 .OH + PC1 5 = C 6 H 5 .CH 2 C1 + POC1 3 + HC1. 

When heated with concentrated acids, or treated with 
anhydrides or acid chlorides, it gives esters ; with hydro- 
bromic acid, for example, it yields benzyl bromide, C 6 H 5 -CH 9 Br 
(b.p. 199), and with acetyl chloride or acetic anhydride it 
gives benzyl acetate, C 6 H 5 .CH 2 .0-CO.CH 3 (b.p. 206). On 
oxidation with dilute nitric acid, it is first converted into 
benzaldehyde and then into benzoic acid, 

C 6 H 5 .CH 2 .OH + = C 6 H 5 .CHO + H 2 
C 6 H 5 .CH 2 .OH + 20 = C 6 H 5 -COOH + H 2 0. 
All these changes are strictly analogous to those undergone 
by the fatty alcohols. 

Saligenin, C 6 H 4 (OH)-CH 2 -OH, also known as o-hydroxybenzyl 
alcohol, or salicyl alcohol, is an example of a substance which 
is both a phenol and an alcohol. It is produced, together with 
glucose, by the action of dilute acids or ferments on salicin, a 
glucoside existing in the bark of the willow-tree, 

Ci 3 H 18 O 7 + H 2 = C 6 H 4 <jj QJJ + C 6 H 12 O 6 . 

It may be prepared synthetically by reducing salicylaldehyde 
(p. 422) with sodium amalgam and alcohol, 



Saligenin melts at 82, and is readily soluble in water, the 
solution acquiring a deep-blue colouration on the addition of ferric 
chloride. Owing to its phenolic nature, it forms alkali salts, which, 
when heated with alkyl halogen compounds, give the corresponding 



KETONES, AND QUINONES. 417 

ethers (the methyl ether, C 6 H 4 (OCH 3 ).CH 2 .OH, is a colourless oil, 
boiling at 247) ; on the other hand, it shows the properties of an 
alcohol, and yields salicylaldehyde and salicylic acid on oxidation. 

The in- and p-hydroxybenzyl alcohols may be prepared by the 
reduction of the in- and ^)-hydroxybenzaldehydes (p. 423) ; they 
melt at 67 and 110 respectively. 

Anisyl alcohol, or^-methoxybenzyl alcohol, C 6 H 4 (OCH 3 )-CH 2 -OH, 
is obtained by treating anisaldehyde, C 6 H 4 (OCH 3 )-CHO (p. 423), 
with sodium amalgam and alcohol or with alcoholic potash. It 
has been prepared synthetically by heating a mixture of jo-hyclroxy- 
benzyl alcohol, potash, and methyl iodide in alcoholic solution at 
100, 

C 6 H 4 < CHs QH + CH 3 I = C 6 H 4 < CH2 ^ H + KI. 

It is crystalline, melts at 25, and boils at 258 ; on oxidation 
it yields anisaldehyde and anisic acid, C 6 H 4 (OCH 3 ).COOH. 



Aldehydes. 

The relation between the aromatic aldehydes and the 
aromatic alcohols is the same as that which exists between 
the corresponding classes of fatty compounds that is to say, 
the aldehydes are derived from the primary alcohols by 
taking away two atoms of hydrogen from the -CH 2 -OH group; 
benzaldehyde, C 6 H 5 -CHO, for example, corresponds with benzyl 
alcohol, C 6 H 5 .CH 2 .OH; salicylaldehyde, C 6 H 4 (OH>CHO, 
withsalicyl alcohol, C 6 H 4 (OH).CH 2 -OH ; phenylacetaldehyde, 
C 6 H 5 .CH 2 .CHO, with phenylethyl alcohol, CeH^CH^CH^OH; 
and so on. 

Now those compounds which contain an aldehyde-group 
directly united with carbon of the nucleus are of far greater 
importance than those in which the aldehyde-group is com- 
bined with a carbon atom of the side-chain, as in phenylacet- 
aldehyde (see above), cinnamic aldehyde, C 6 H 5 -CH:CH-CHO, 
&c. ; whereas, moreover, the latter resemble the fatty alde- 
hydes very closely in general character, and do not therefore 
require any detailed description, the former differ from the 
fatty compounds in several important particulars, as will be 
seen from the following account of benzaldehyde and salicyl- 

Org. Cbein. 2 A 



418 AROMATIC ALCOHOLS, ALDEHYDES, 

aldehyde, two of the best-known aromatic compounds which 
contain the aldehyde group directly united with the benzene 
nucleus. 

Benzaldehyde, C 6 H 5 -CHO, sometimes called 'oil of bitter 
almonds,' was formerly obtained from the glucoside (compare 
foot-note, Part I. p. 287), amygdalin, which occurs in bitter 
almonds, and which, in contact with water, gradually under- 
goes decomposition into benzaldehyde, hydrogen cyanide, and 
glucose. 

Benzaldehyde may be obtained by oxidising benzyl alcohol 
with nitric acid, and by distilling a mixture of calcium 
benzoate and calcium formate, 

(C 6 H 5 -COO) 2 Ca + (H-COO) 2 Ca = 2C 6 H 5 -CHO + 2CaC0 8 , 
reactions analogous to those employed in the fatty series. 

It is prepared both in the laboratory and on the large scale 
either by heating benzal chloride (p. 362) with moderately 
dilute sulphuric acid, or calcium hydroxide, under pressure, 
or by boiling benzyl chloride with an aqueous solution of lead 
nitrate or copper nitrate. In the first method, the benzal 
chloride is probably first converted into the corresponding 
dihydroxy-derivative of toluene, 

C 6 H 5 .CHC1 2 + 2H 2 = C 6 H 5 .CH(OH) 2 + 2HC1 ; 
but as this compound contains two hydroxyl-groups united 
with one and the same carbon atom, it is very unstable (Part I. 
p. 129, foot-note), and subsequently undergoes decomposition 
into benzaldehyde and water. In the second method, the 
benzyl chloride is probably transformed into benzyl alcohol, 
which is then oxidised to the aldehyde by the metallic nitrate, 
with evolution of oxides of nitrogen and formation of copper 
or lead chloride, as indicated by the equation, 
2C 6 H 5 -CH 2 .OH + Cu(N0 8 ) 2 + 2HC1 = 

2C 6 H 5 .CHO + CuCl 2 + N 2 3 + 3H 2 0. 

Benzyl chloride (5 parts), water (25 parts), and copper nitrate 
(4 parts) are placed in a flask connected with a reflux condenser, 
and the mixture is boiled for six to eight hours, a stream of carbon 



KETONES, AND QUINONES. 419 

dioxide being passed into the liquid all the time, in order to expel 
the oxides of nitrogen, which would otherwise oxidise the benz- 
aldehyde to benzoic acid ; the process is at an end when the oil 
contains only traces of chlorine, which is ascertained by washing 
a small portion with water, and boiling it with silver nitrate 
arid nitric acid. The benzaldehyde is then extracted with ether, 
the ethereal extract shaken with a concentrated solution of 
sodium bisulphite, and the crystals of the bisulphite compound, 
C 6 H 5 -CHO, NaHS0 3 , separated by filtration and washed with 
ether ; the benzaldehyde is then regenerated by decomposing the 
crystals with dilute sulphuric acid, extracted with ether, and 
distilled. 

Benzaldehyde is a colourless, highly refractive liquid of 
sp. gr. 1-05 at 15; it boils at 179, and is volatile in steam. 
It has a pleasant smell like that of bitter almonds, and is 
only sparingly soluble in water, but miscible with alcohol, 
ether, &c., in all proportions. It is extensively used for 
flavouring purposes, and is employed on the large scale in 
the manufacture of various dyes. 

Benzaldehyde, and aromatic aldehydes in general, resemble 
the fatty aldehydes in the following respects : They readily 
undergo oxidation, sometimes merely on exposure to the air, 
yielding the corresponding acids, 

C 6 H 5 -CHO + = C 6 H 5 -COOH, 

and consequently they reduce ammoniacal solutions of silver 
hydroxide. On reduction they are converted into the 
corresponding alcohols, 

C 6 H 6 .CHO + 2H = C 6 H 5 -CH 2 .OH. 

When treated with phosphorus pentachloride, they give 
dihalogen derivatives such as benzal chloride, C 6 H 5 -CHC1 2 , 
two atoms of chlorine being substituted for one atom 
of oxygen. They interact with hydroxylamine, yielding 
aldoximes, and with phenylhydrazine, giving hydrazones, 
C 6 H 5 -CHO + NH 2 -OH = H 2 + C 6 H 5 -CH:N.OH 

Benzalcloxime. 

C 6 H 5 .CHO + NH 2 .NH.C 6 H fi = H 2 + C 6 H 6 -CH:N 2 H.C 6 H 6 . 

Benzylidenehydrazone. 



420 AROMATIC ALCOHOLS, ALDEHYDES, 

They combine directly with sodium bisulphite, forming 
crystalline compounds, and with hydrogen cyanide they 
yield hydroxycyanides such as benzylidenehydroxycyanide* 
C 6 H 5 -CH(OH)-CN. They readily undergo condensation 
with many other fatty and aromatic compounds ; when, for 
example, a mixture of benzaldehyde and acetone is treated 
with a few drops of soda at ordinary temperatures, condensa- 
tion occurs, and benzylideneacetone, C 6 H 5 -CH:CH-CO-CH 3 
(m.p. 42), is formed. 

Benzaldehyde, and other aromatic aldehydes which contain 
the -CHO group directly united with the benzene nucleus, 
differ from the fatty aldehydes in the following respects : 
They do not reduce Fehling's solution, and they do not 
undergo polymerisation; they do not form additive com- 
pounds with ammonia, but yield complex products such 
as hydrobenzamide, (C 6 H 5 -CH) 3 N 2 , which is obtained by 
treating benzaldehyde with ammonia. When shaken with 
concentrated potash (or soda) they yield a mixture of the 
corresponding alcohol and acid (compare p. 415), 

2C 6 H 5 .CHO + KOH - C 6 H 5 .CH 2 .QH + C 6 H 5 -COOK. 

When benzaldehyde (5 parts) is heated with a solution of 
potassium cyanide (1 part) in aqueous alcohol for about an hour, 
it is converted into benzoin, which separates on cooling in colour- 
less crystals ; benzoin is a ketonic alcohol, formed in accordance 
with the equation, 



it melts at 137, and is oxidised hy boiling concentrated nitric acid, 
giving a diketone, benzil, C 6 H 5 -CO-CO-C 6 H 5 , which is yellow and 
melts at 95. 

Nitrobenzaldehydes, C 6 H 4 (N0 2 )- CHO. When treated with a 
mixture of nitric and sulphuric acids, benzaldehyde yields w-nitro- 
benzaldehyde (m.p. 58) as principal product, small quantities of 
o-nitrobenzaldehyde (m.p. 46) being formed at the same time. 

jo-Nitrobenzaldehyde (m.p. 107), and also the o-compound, are 
most conveniently prepared by the oxidation of the corresponding 
nitrocinnamic acids (p. 445) with potassium permanganate, 

* The name benzylidene is given to the group of atoms, C 6 H 5 -CH=, 
which is analogous to ethylidene, CH 3 -CH= (Part I. p. 142). 



RETONES, AND QTJINONES. 421 



During the operation the mixture is shaken with benzene in order 
to extract the aldehyde as fast as it is formed, and thus prevent 
it from being further oxidised. The benzene solution is then 
evaporated, and the aldehyde purified by recrystallisation. 

The nitrobenzaldehydes are colourless, crystalline substances, 
which show much the same behaviour as benzaldehyde itself; when 
reduced with ferrous sulphate and ammonia they are converted into 
the corresponding amidobenzaldehydes, C 6 H 4 (NH 2 )-CHO. 

o-Nitrobenzaldehyde is a particularly interesting substance, as, 
when its solution in acetone is mixed with a few drops of dilute 
soda, a precipitate of indigo-Uue gradually forms (Baeyer). This 
important synthesis of this vegetable dye may be represented by 
the equation, 



Indigo-blue. 

+2CH 3 .COOH + 2H 2 0. 



Hydroxy-aldehydes. 

The hydroxy-derivatives of the aldehydes, such as the 
hydro xybenzaldehydes, C 6 H 4 (OH)-CHO, which contain the 
hydroxyl-group united with the nucleus, combine the pro- 
perties of phenols and aldehydes. 

They may be obtained by the oxidation of the correspond- 
ing hydroxy-alcohols ; saligenin (p. 416), or o-hydroxybenzyl 
alcohol; for example, yields salicylaldehyde or o-hydroxybenz- 
aldehyde, 



As, however, such alcohols are not easily obtained, and indeed 
in many cases have only been produced by the reduction of 
the hydroxy-aldehydes, the latter are usually prepared by 
heating the phenols with chloroform in alkaline solution 
(Keimer's reaction), 

C 6 H 5 -OH + CHC1 3 + 3KOH = C 6 H 4 < + 3KC1 + 2H 2 0. 



422 AROMATIC ALCOHOLS, ALDEHYDES, 

The actual changes which occur in carrying out Reimer's reaction 
are not clearly understood ; possibly the phenol interacts with the 
chloroform, in the presence of the alkali, yielding an intermediate 
product containing halogen, 

+ HC1, 



which by the further action of the alkali is converted into a 
'hydroxybenzaldehyde, just as benzalchloride, C 6 H 5 -CHC1. 2 , is trans- 
formed into benzaldehyde (compare p. 418), 

OH /OH /OH 



As a rule, the principal product is the o-hydroxyaldehyde, small 
quantities of the corresponding p-compound being produced at the 
same time. 

Salicylaldehyde (<?-hydroxybenzaldehyde), C 6 H 4 (OH)-CHO, 

may be obtained by oxidising saligenin with chromic acid (see 
above), but it is usually prepared from phenol by Reimer's 
reaction. 

Phenol (20 grams) is dissolved in caustic soda (60 grams) and 
water (120 grains), the solution heated to 60 in a flask provided 
with a reflux condenser, and chloroform (30 grams) added in small 
quantities at a time from a dropping funnel. After slowly heating 
to boiling, the unchanged chloroform is distilled off, the alkaline 
liquid acidified and distilled in steam, when a mixture of phenol 
and salicylaldehyde passes over. (The residue in the flask con- 
tains |?-hydroxybenzaldehyde, which may be extracted from the 
filtered liquid with ether, and purified by recrystallisation. ) The 
oily mixture is extracted from the distillate with ether, and the 
extract shaken with a solution of sodium bisulphite, which dis- 
solves the aldehyde in the form of its bisulphite compound. The 
solution is then separated, decomposed with sodium carbonate, and 
the regenerated salicylaldehyde extracted with ether and purified 
by distillation. 

Salicylaldehyde is a colourless oil which boils at 196, 
and has a penetrating, aromatic odour ; it is moderately 
soluble in water, its solution giving a deep violet colouration 
with ferric chloride. When reduced with sodium amalgam it 
yields saligenin, C 6 H 4 (OH>CH 2 .OH (p. 416), whereas oxidis- 
ing agents convert it into salicylic acid, C 6 H 4 (OH)-COOH. 



KETONES, AND QUINONES. 423 

p-Hydroxybenzaldehyde melts at 116; it dissolves readily in hot 
water, and gives, with ferric chloride, a violet colouration. 

m-Hydroxybenzaldehyde is obtained by converting w-nitrobenzal- 
dehyde into w-amidobenzaldehyde, and then displacing the amido- 
group by hydroxyl, by means of the diazo-reaction. It crystallises 
from water in needles, and melts at 104. 

Anisaldehyde (^-methoxybenzaldehyde), C 6 H 4 (OCH 3 )-CHO, 
is prepared from oil of aniseed. This ethereal oil contains 
anetkole, C 6 H 4 (OCH 3 ).CH:CH-CH 3 , a crystalline substance 
(m.p. 21 C ), which on oxidation with potassium dichromate 
and sulphuric acid is converted into anisaldehyde, the pro- 
penyl group -CH:CH-CH 3 being oxidised to the aldehyde 
group. It may be prepared synthetically by digesting 
j9-hydroxybenzaldehycle with alcoholic potash and methyl 
iodide, 

C <ft<CHO + CH ^ = C A<CH0 3 + KL 

Anisaldehyde boils at 248, and has a penetrating, aromatic 
odour ; on reduction with sodium amalgam it yields anisyl 
alcohol, C 6 H 4 (OCH 3 ).CH 2 -OH (p. 417); oxidising agents 
convert it into anisic acid, C 6 H 4 (OCH 3 ).COOH (p. 452). 

Ketones. 

The ketones of the aromatic, like those of the fatty series, 
have the general formula R-CO-R', where R and R' re- 
present different or identical radicles, one of which must, of 
course, be aromatic. 

Acetophenone, phenylmethyl ketone, or acetylbenzene, 
C 6 H 5 -CO-CH 3 , may be described as a typical aromatic ketone. 
It is formed on distilling a mixture of calcium benzoate and 
calcium acetate, a reaction which is exactly analogous to that 
which is made use of in obtaining mixed ketones of the fatty 
series, 

(C 6 H 6 .COO) 2 Ca + (CH 3 -COO) 2 Ca = 2C 6 H 5 -GO.CH 3 + 2CaC0 3 . 
It is most conveniently prepared by dropping acetyl chloride 



424 AROMATIC ALCOHOLS, ALDEHYDES, 

(1 mol.) into well-cooled benzene (1 mol.) in presence of 
aluminium chloride, 

C 6 H 6 + CH 3 .COC1 = C 6 H 5 .CO-CH 3 + HC1. 

This method is of general use, as by employing other acid 
chlorides and other hydrocarbons, many other ketones maybe 
prepared ; it is an extension of Friedel and Crafts' method of 
preparing hydrocarbons (p. 340). 

Acetophenone melts at 20-5, and boils at 202 ; it is used 
as a hypnotic in medicine, under the name of hypnone. Its 
chemical behaviour is so similar to that of the fatty ketones 
that most of its reactions, or at any rate those which are 
determined by the carbonyl-group, might be foretold from a 
consideration of those of acetone ; on reduction with sodium 
amalgam and aqueous alcohol, acetophenone is converted into 
phenylmethyl carbinol, C 6 H 5 -CH(OH)-CH 3 , just as acetone is 
transformed into isopropyl alcohol ; like acetone, and other 
fatty ketones, it interacts with hydroxylamine and with 
phenylhydrazine, giving the oxime, C 6 H 5 -C(NOH)-CH 3 , and 
the hydrazone, C 6 H 5 .C(N 2 HC 6 H 5 )-CH 3 , respectively. On 
oxidation it is resolved into benzoic acid and carbon dioxide, 
just as acetone is oxidised to acetic acid and carbon dioxide, 

C 6 H 5 .CO-CH 3 + 40 = C 6 H 5 .COOH + C0 2 + H 2 0. 

Acetophenone shows also the general behaviour of aromatic 
compounds, inasmuch as it may be converted into nitro-, 
amido-, and halogen-derivatives by displacement of hydrogen 
of the nucleus. 

The homologues of acetophenone, such as propiophenone, 
C 6 H 5 -CO-C 2 H 5 , butyrophenone, C 6 H 5 .CO-C 3 H 7 , &c., are of 
little importance, but benzophenone, an aromatic ketone of a 
different series, may be briefly described. 

Benzophenone, diphenyl ketone, or benzoylbenzene, 
C 6 H 5 -CO-C 6 H 5 , may be obtained by distilling calcium 
benzoate, arid by treating benzene with benzoyl chloride, 
or with carbonyl chloride, in presence of aluminium chloride, 



KETONES, AND QUINONES. 425 

C 6 H 6 + C 6 H 5 -COC1 = C 6 H 5 .CO-C 6 H 5 + HC1 

2C 6 H 6 + COC1 2 = C 6 H 5 .CO.C 6 H 5 + 2HC1. 

It melts at 48-49, and is very similar to acetophenone in 

most respects ; when distilled over zinc-dust it is converted 

into diphenylmethane, C 6 H 5 -CH 2 -C 6 H 5 (p. 351). 

Quinones. 

When hydroquinone is oxidised with excess of ferric 
chloride in aqueous solution a yellowish colouration is pro- 
duced, and the solution acquires a very penetrating odour ; 
if sufficiently strong, yellow crystals are deposited. 

The substance formed in this way is named quinone (benzo- 
quinone), and is the simplest member of a very interesting 
class of compounds ; its formation may be expressed by the 
equation, 

C 6 H 4 (OH) 2 + = C 6 H 4 2 + H 2 0. 

Quinone, C 6 H 4 2 , is usually prepared by oxidising aniline 
with potassium dichromate and sulphuric acid. 

Aniline (1 part) is dissolved in water (25 parts) and sulphuric 
acid (8 parts), and finely-powdered potassium dichromate (3-5 parts) 
gradually added, the whole being well cooled and constantly stirred 
during the operation ; the product, which is very dark-coloured 
owing to the presence of aniline black, may be extracted with 
ether, but is more conveniently isolated by submitting the liquid, 
in small portions at a time, to steam distillation, as rapidly as 
possible. The quinone is then separated by filtration, the filtrate 
being extracted with ether if necessary. 

Quinone crystallises in golden-yellow prisms, melts at 116, 
sublimes very readily, and is volatile in steam; it has a 
peculiar, irritating, and very characteristic smell, and is only 
sparingly soluble in water, but dissolves freely in alcohol and 
ether. It is readily reduced by sulphurous acid, zinc and 
hydrochloric acid, &c., being converted into hydroquinone, 



In some respects quinone behaves as if it contained two 
carbon yl-groups, each having properties similar to those of the 



426 AROMATIC ALCOHOLS, ALDEHYDES, 

carbonyl-groups in compounds such as acetone, acetophenone, 
&c. ; when treated with hydroxylamine hydrochloride, for 

example, quinone yields a monoxime, C 6 H 4 ^f ^ ^^ (identical 



with ^>-nitrosophenol, p. 379), and also a dioxime, C 6 H 4 <,,. , 



The two carbonyl-groups, moreover, are in the jpara-position 
to one another, as is shown by the facts that when quinone 
is reduced it gives hydroquinone (/?aro-dihydroxy benzene), 
and when quinone-dioxime is reduced with tin and hydro- 
chloric acid it yields ^-phenylenediamine (p. 376). 

In other respects, however, quinone undergoes changes 
which are quite different from those observed in the case 
of ordinary ketones ; on reduction, for instance, each >CO 
group is transformed into ^>C-OH, and not into >CH-OH, 
as might have been expected from analogy ; again, on treat- 
ment with phosphorus pentachloride, each oxygen atom is 
displaced by one atom of chlorine, jp-dichlorobenzene, C 6 H 4 C1 2 , 
being formed, and not a tetrachloro-derivative, as might have 
been expected. 

This curious behaviour, and the close relation between 
hydroquinone and quinone, is explained by assuming that in 
the conversion of the former into the latter by oxidation 
intramolecular change also takes place, and in such a way as 
to bring about a rearrangement of the carbon affinities. On 
reducing quinone, or on treating it with phosphorus penta- 
chloride, this change is reversed, and the condition represented 
by the centric formula is again established ; the following 
formulas indicate the nature of these changes, 



OH 





in 

Hydroquiuone. Quiuoiio. Dichloroben/eue. 




KETONES, AND QUINONES. 427 

The constitution of quinone may also be represented by the 
following formula, 




which was first suggested by Graebe, arid which does not necessi- 
tate the view that intramolecular change occurs in the conversion 
of quinone into hydroquinone. If this formula be adopted, the 

/N.OH 

constitution of quinone monoxime would be, C 6 H 4 < I , and 

the formation of this compound from jo-nitrosodimethylaniline 
(p. 379) would involve no change in the nucleus; if, however, 

quinone be really a diketone, C 6 H 4 <^Q, its monoxime would be 

C 6 H 4 <f ' , and intramolecular change must be assumed to 

occur during its formation from j9-nitrosodimethyl aniline. The 
principal arguments which can be advanced in favour of the 
diketone formula are, firstly, that quinone gives a dioxime, and 
secondly, that it combines directly with bromine, giving a di- and a 
tetra-brornide, C 6 H 4 Br 2 2 and C 6 H 4 Br 4 O 2 . The latter behaviour 
seems to show that the carbon atoms in quinone are united in the 
same way as those in unsaturated compounds, such as ethylene, 
and not as those in benzene and its ordinary substitution products 
(compare p. 336). 

Benzoquinone and many other para-quinones (that is to say, 
quinones in which the two carbonyl-groups are in the para- 
position to one another *) may he produced by the oxidation, 
with chromic acid or ferric chloride, of many hydroxy- and 
amido-compounds, which contain the substituting groups in the 
para-position ; quinone, for example, is formed on oxidising 
aniline, p-amidophenol, C 6 H 4 (OH)-NH 2 , and >-phenylene- 
diamine, C 6 H 4 (NH 2 ) 2 , whereas o-toluidine and j9-toluylene- 
diamine, CgH^NH^-CHg, [NH 2 :1S T H 2 :CH 3 = 1:4:2], yield 
toluquinone [0:0: CH 3 = 1:4:2]. All joara-quinones resemble 

* Other quinones, of a somewhat different class from benzoquinone, are 
described later (pp. 468, 483). 



428 AROMATIC ALCOHOLS, ALDEHYDES, ETC. 

(benzo)quinone in smell, in having a yellow colour, and in 
being readily volatile. 

When bleaching-powder is used in oxidising amido-compoimda 
such as the above, quinone chlorimides and quinone dichloro- 
diimides are formed in the place of quinones, 

NH 2 .C 6 H 4 .OH + 4C1 = NC1:C 6 H 4 :O + 3HC1 

Quinone Chlorimide. 
NH 2 -C 6 H 4 .NH 2 + 6C1 = NCI: C 6 H 4 : NCI + 4HC1. 

Quinone Dichlorocliimide. 

The quinone chlorimides and dichlorodiimides resemble quinone 
in many respects ; they are crystalline, readily volatile in steam, 
and are respectively converted into jo-amidophenol andj^-phenylene- 
diamine or their derivatives on reduction. 

Chloranil, or tetrachloroquinone, O:C 6 C1 4 :O, is produced when 
chlorine acts on quinone, but it is usually prepared by treating 
phenol with hydrochloric acid and potassium chlorate, oxidation 
and chlorination taking place simultaneously, 

C 6 H 5 .OH + 10C1 + O = O:C 6 C1 4 :0 + 6HC1. 

It crystallises in yellow plates, sublimes without melting, and is 
sparingly soluble in alcohol, and insoluble in water. 

It is readily reduced to tetrachlorohydroquinone, HO-C 6 C1 4 -OH, 
and is therefore a powerful oxidising agent, for which reason it is 
much employed in colour chemistry, when the use of inorganic 
oxidising agents is undesirable. 



CHAPTER XXIX. 

CARBOXYLIC ACIDS. 

The carboxylic acids of the aromatic series are derived from 
the aromatic hydrocarbons, just as those of the fatty series 
are derived from the paraffins namely, by the substitution of 
one or more carboxyl-groups for a corresponding number of 
hydrogen atoms. In this, as in other cases, however, one 
of two classes of compounds may be obtained according as 
substitution takes place in the nucleus or in the side-chain ; 
benzene yields, of course, only acids of the first class, such as 
benzoic acid, C 6 H 6 -COOH, the three (o.m.p.) plitlialic acids, 



CARBOXYLIC ACIDS. 429 

C 6 H 4 (COOH) 2 , the three tricarboxylic acids, C 6 H 3 (COOH) 3 , 
&c., but toluene (and all the higher homologues) may give 
rise to derivatives of both kinds as, for example, the 
three toluic acids, C 6 H 4 (CH 3 )-COOH, and phenylacetic acid, 
C 6 H 5 -CH 2 .COOH. 

Although there are no very important differences in the 
properties of these two classes of acids, it is more convenient 
to describe them separately, taking first those compounds in 
which the carboxyl-groups are directly united with carbon 
of the nucleus. 

Preparation. Such acids may be obtained by oxidising 
the alcohols or aldehydes, 

C 6 H 5 .CH 2 .OH + 20 = C 6 H 5 .COOH + H 2 
C 6 H 5 .CHO + = C 6 H 5 .COOH, 

and by hydrolysing the nitriles (p. 433) with alkalies or 
mineral acids, 

C 6 H 5 .Ctf + 2H 2 = C 6 H 5 .COOH + NH 3 
C 6 H 5 .CH 2 .CN + 2H 2 = C 6 H 5 -CH 2 .COOH + NH 3 , 

reactions which are exactly similar to those employed in the 
case of the fatty acids (Part I. p. 168). 

Perhaps, however, the most important method, and one 
which has no counterpart in the fatty series, consists in 
oxidising the homologues of benzene with dilute nitric acid 
or chromic acid, 

C 6 H 5 .CH 3 + 30 = C 6 H 5 .COOH + H 2 O 
C 6 H 5 .CH 2 -CH 3 + 60 = C 6 H 5 .COOH + C0 2 + 2H 2 0. 

In this way only those acids which contain the carboxyl-group 
united with the nucleus can be obtained, because the side-chain 
is always oxidised to -CO OH, no matter how many -CH 2 - 
groups it may contain ; in other words, all homologues of 
benzene which contain only one side-chain yield benzoic acid, 
whereas those containing two give one of the phthalic acids. 
In the latter case, however, one of the side-chains may be 
oxidised before the other is attacked, so that by stopping the 



430 CARBOXYLIG ACIDS. 

process at the right time, an alkyl-derivative of benzoic acid is 
first obtained, 

C 6 H 4 (CH 3 ), + 30 = C 6 H 4 (CH 3 ) -COOK + H 2 
C 6 H 4 (CH 3 >COOH + 30 = C 6 H 4 (COOH) 2 + H 2 0. 

Oxidation is frequently carried out by boiling the hydrocarbon 
(1 vol.) with nitric acid (1 vol.) diluted with water (2-4 vols.) until 
brown fumes are no longer formed. The mixture is then made 
slightly alkaline with soda, and any unchanged hydrocarbon and 
traces of nitro- hydrocarbon separated by distilling with steam or by 
extracting with ether; the alkaline solution is then acidified and 
the acid separated by filtration and purified by recrystallisation. 

Most hydrocarbons are only very slowly attacked by oxidising 
agents generally, and it is often advantageous to first substitute 
chlorine or some other group for hydrogen of the side-chain, as in 
this way oxidation is facilitated. Benzyl chloride, C 6 H 5 -CH 2 C1, and 
benzyl acetate, C 6 H 5 -CH 2 -OC 2 H 3 (p. 361), for example, are much 
more readily oxidised than toluene, because they first undergo 
hydrolysis, giving alcohols. 

Properties. The aromatic acids are crystalline, and gener- 
ally distil without decomposing; they are sparingly soluble 
in cold water, but much more readily in hot water, alcohol, 
and ether. As regards, all those properties which are deter- 
mined by the carboxyl-group, the aromatic acids are closely 
analogous to the fatty compounds, and give corresponding 
derivatives, as the following examples show, 

Benzoic acid, C 6 H 5 .COOH Benzoyl chloride, C 6 H 5 -COC1 
Sodium benzoate, C 6 H 5 -COONa Benzamide, C 6 H 5 .CO-NH 2 

Ethyl berizoate, C 6 H 5 .COOC 2 H 5 Benzoic anhydride, (C 6 H 5 -CO) 2 0. 

When distilled with lime, they are decomposed with loss of 
carbon dioxide and formation of the corresponding hydro- 
carbons, just as acetic acid under similar circumstances yields 
marsh-gas, 

C 6 H 5 .COOH = C 6 H 6 + C0 2 
C 6 H 4 (CH 3 )-COOH = C 6 H 5 -CH 3 + C0 2 . 

Benzoic acid, C 6 H 5 -COOH, occurs in the free state in 
many resins, especially in gum benzoin and Peru balsam ; it 
is also found in the urine of cows and horses, as hippuric acid 






CARBOXYLIC ACIDS. 431 

or benzoylglycine, C 6 H 5 -CO-NH.CH 2 .COOH, to the extent of 
about 2 per cent. 

It may be obtained by subliming gum benzoin in iron pots, 
the crude sublimate being purified by recrystallisation from 
water ; or by boiling hippuric acid with hydrochloric acid 
(Parti, p. 300), 
C 6 H 5 -CO.]mCH 2 .COOH + HC1 + H = 



, HC1. 

Benzoic acid is manufactured by oxidising benzyl chloride 
(p. 361) with 60 per cent, nitric acid, 

C 6 H 5 .CH 2 C1 + 20 = C 6 H 5 .COOH + HC1, 
or by heating calcium phthalate with lime at about 350, 

2C 6 H 4 (COO) 2 Ca + Ca(OH) 2 = (C 6 H 5 .COO) 2 Ca + 2CaC0 3 . 
It may also be prepared by oxidising toluene, benzyl alcohol, 
or benzaldehyde, and by hydrolysing benzonitrile with caustic 
soda, 

C 6 H 5 .CO.(m + 2H 2 = C 6 H 5 .COOH + NH 3 . 

Benzoic acid separates from water in glistening crystals, 
melts at 121-5, and boils at 249, but it sublimes very readily 
even at 100, and is volatile in steam ; it dissolves in 400 
parts of- water at 15, but is readily soluble in hot water, 
alcohol, and ether. Its vapour has a characteristic odour, 
and an irritating action on the throat, causing violent 
coughing. Most of the metallic salts of benzoic acid 
are soluble in water and crystallise well ; calcium benzoate, 
(C H 5 -COO) 2 Ca + 3H 2 0, for example, prepared by neutralis- 
ing benzoic acid with milk of lime, crystallises in needles, 
and is very soluble in water. 

Ethyl benzoate, C 6 H 5 -COOC 2 H 5 , is prepared by saturating 
a solution of benzoic acid (1 part) in alcohol (3 parts) with 
hydrogen chloride, and then boiling the solution (with reflux 
condenser) for about two hours (Part I. p. 191). 

The alcohol is then distilled, the oily residue poured into water, 
and shaken with dilute sodium carbonate until free from acids ; the 
ester is next washed with water, dried with calcium chloride, and 



432 CARBOXYLIC ACIDS. 

distilled. A little ether may be used to dissolve the ester if it does 
not separate well from the aqueous solutions. It boils at 211, has 
a pleasant aromatic odour, and is readily hydrolysed by boiling 
alcoholic potash. 

Benzoyl chloride, C 6 H 5 -COC1, is obtained by treating 
benzoic acid with phosphorus pentachloride. 

The dry acid is placed in a distillation flask, and about 5 per cent, 
more than one molecular proportion of the pentachloride is added ; 
the fumes which are evolved are passed into water or dilute soda 
(care being taken that the liquid is not sucked into the flask), the 
whole operation being conducted in the fume cupboard. When the 
reaction is finished, the mixture of phosphorus oxychloride (b.p. 
107) and benzoyl chloride is submitted to fractional distillation. 

It is a colourless oil, possessing a most irritating odour, 
and boils at 198; it is gradually decomposed by water, 
yielding benzoic acid and hydrochloric acid. 

Benzoic anhydride, (C 6 H 5 -CO) 2 0, is produced when benzoyl 
chloride is treated with sodium benzoate, just as acetic anhy- 
dride is formed by the interaction of acetyl chloride and 
sodium acetate (Part I. p. 163); it is a crystalline substance, 
melting at 42, and closely resembles acetic anhydride in 
ordinary chemical properties. 

Benzoyl chloride and benzoic anhydride, more especially 
the former, are frequently used for the detection of hydroxy- 
and amido-compounds, as they interact with all such sub- 
stances, yielding benzoyl-derivatives, the monovalent lenzoyl- 
group, C 6 H 5 -CO-, taking the place of the hydrogen of the 
hydroxyl- or amido-group, 

C 6 H 5 -COC1 + C 2 H 5 .OH = C 6 H 5 .O.CO-C 2 H 5 + HC1 

Ethyl Benzoate. 

(C 6 H 5 .CO) 9 + C 2 H 5 -OH = C 2 H 5 -O.CO.C 6 H 5 + C 6 H 5 -COOH 

C 6 H 5 .COC1 + NH 2 -C 6 H 5 = C 6 H 5 .CO-NH.C 6 H 5 + HC1. 
As such benzoyl-derivatives usually crystallise much more 
readily than the corresponding acetyl-derivatives, they are 
generally prepared in preference to the latter when it is a 
question of identifying or isolating a substance. 



CARBOXYLIC ACIDS. 433 

Benzoyl-derivatives may be prepared by heating the hydroxy- 
or amido-compound with benzoyl chloride or with benzoic anhy- 
dride. A more convenient method, however, is that of Baumann 
and Schotten : it consists in adding benzoyl chloride and 10 per cent. 
potash alternately, in small quantities at a time, to the compound, 
which is either dissolved or suspended in water, the mixture being 
well shaken and kept cool during the operation. Potash alone is 
then added until the disagreeable smell of benzoyl chloride is no 
longer noticed, and the solution remains permanently alkaline; 
the product is finally separated by filtration or by extraction with 
ether. The alkali serves to neutralise the hydrochloric acid which 
is formed, the interaction taking place much more readily in the 
neutral or slightly alkaline solution. 

Benzamide, C 6 H 5 -CO-NH 2 , may be taken as an example of 
an aromatic amide ; it may be obtained by reactions similar 
to those employed in the case of acetamide (Part I. p. 164), 
as, for example, by treating ethyl benzoate with ammonia, 
C 6 H 5 -COOC 2 H 5 + NH 3 = C 6 H 5 .CO-NH 2 + C 2 H 5 -OH ; 
but it is most conveniently prepared by triturating benzoyl 
chloride with excess of dry ammonium carbonate in a mortar 
until the smell of the chloride is barely perceptible, and then 
purifying the product by recrystallisation from water, 



C 6 H 5 .CO-NH 2 + C0 2 + H 

It is a crystalline substance, melts at 130, and is sparingly 
soluble in cold, .but readily soluble in hot, water ; like other 
amides, it is decomposed by boiling alkalies, yielding ammonia 
and an alkali salt, 

C 6 H 5 .CO-NH 2 + KOH = C 6 H 5 -COOK + NH 3 . 

Benzonitrile, or phenyl cyanide, C 6 H 5 -CN, may be obtained 
by treating benzamide with dehydrating agents, a method 

similar to that employed in the preparation of fatty nitriles, 
C 6 H 6 .CO-NH 2 = C 6 H 5 .CN + H 2 0. 
Although it cannot be prepared by treating chloro- or bromo- 
benzene with potassium cyanide (the halogen atom being so 
firmly held that no interaction occurs), it may be obtained by 



Org, Chem. 2 B 



434 CARBOXYLIC ACIDS. 

fusing benzenesulphonic acid with potassium cyanide (or with 
potassium ferrocyanide, which yields the cyanide), just as 
fatty nitriles may be prepared by heating the alky Isulph uric 
acids with potassium cyanide, 

C 6 H 5 .S0 3 K + KCN = C 6 H 5 -CN + K 2 S0 3 



C 2 H 6 .S0 4 K + KCN = C 2 H 5 -CN + K 2 S0 4 . 

It is, however, most conveniently prepared from aniline by 
Sandmeyer's reaction namely, by treating a solution of diazo- 
benzene chloride with cuprous cyanide (p. 384), 

C 6 H 5 .N 2 C1 + CuCN = C 6 H 5 -CN + CuCl + N^ 

Aniline (1 part) is diazotised exactly as already described (p. 384), 
and the solution of the diazo-chloride is then gradually added 
to a hot solution of cuprous cyanide (see below) ; the product is 
separated by steam distillation, &c., just as described in the 
case of iodobenzene (p. 358). 

The solution of cuprous cyanide is prepared by slowly adding a 
solution of potassium cyanide (3 parts) to a solution of crystallised 
cupric sulphate (2^ parts), this and the subsequent operations, 
including steam distillation, being conducted in a good draught 
cupboard on account of the evolution of cyanogen and hydrogen 
cyanide, 

2CuSO 4 + 4KCN = 2CuCN + (CN) 2 + K 2 SO 4 . 

Benzonitrile is a colourless oil, boiling at 191, and smells like 
nitrobenzene. It undergoes changes exactly similar to those 
which are characteristic of fatty nitriles, being converted into 
the corresponding acid on hydrolysis with alkalies or mineral 
acids, 

C 6 H 6 .CE" + 2H 2 = C 6 H 5 -COOH + NH 3 , 
and into a primary amine on reduction, 

C 6 H 5 -CN + 4H - C 6 H 5 .CH 2 .NH 2 . 

Other aromatic nitriles, such as the three tolunitriles, 
C 6 H 4 (CH 3 )-CN~, are known, also compounds such as phenyl- 
acetonitrile (benzyl cyanide, p. 442), C 6 H 5 -CH 2 -CN, which 
contain the cyanogen group in the side-chain. 

Substitution Products of Benzole, Acid. Ben zoic acid is 
attacked by halogens (although not so readily as the hydro- 



CABBOXYLIC ACIDS. 435 

carbons), the first product consisting of the ??^eta-derivative 
(p. 364) ; when, for example, benzoic acid is heated with bromine 
and water at 125, ra-bromobenzoic acid, C 6 H 4 Br-COOH (m.p. 
155), is formed. The o- and ^>-bromobenzoic acids are obtained 
by oxidising the corresponding bromotoluenes with dilute 
nitric or chromic acid; the former melts at 147, the latter 
at 251. Nitric acid, in the presence of sulphuric acid, acts 
readily on benzoic acid, m-nitrobenzoic acid, C 6 H 4 (N0 2 )-COOH 
(m.p. 141), being the principal product; o-nitrobenzoic acid 
(m.p. 147) and j9-nitrobenzoic acid (m.p. 238) are obtained 
by the oxidation of o- and ^>-nitrotoluene respectively 
(p. 367) ; when these acids are reduced with tin and hydro- 
chloric acid, they yield the corresponding amidobenzoic acids, 
C 6 H 4 (NH 2 )-COOH, which, like giycine (Part I. p. 299), form 
salts both with acids and bases. 

Anthranilic acid, or o-amidobenzoic acid, was first obtained 
by oxidising indigo (p. 539); it melts at 144, and decom- 
poses at higher temperatures, giving aniline and carbon 
dioxide. 

When heated with sulphuric acid, benzoic acid is converted into 
m-sulphobenzoic acid, C 6 H 4 (S0 3 H)-COOH, small quantities of the 
j9-acid also being produced. The o-acid is obtained by oxidising 
toluene-o-sulphonic acid ; when treated with ammonia it yields an 
imide (p. 439), 



which is remarkable for possessing an exceedingly sweet taste, and 
which is known as saccharin. 

The sulphobenzoic acids are very soluble in water ; when fused 
with potash they yield hydroxy-acids (p. 446), just as benzene- 
sulphonic acid gives phenol, 

C 6 H 4 (S0 3 K).COOK + 2KOH = C 6 H 4 (OK) COOK + K 2 SO 3 + H 2 O. 

The three (o.m.p.) toluic acids, C 6 H 4 (CH 3 )-COOH, may be 
produced by oxidising the corresponding xylenes with dilute 
nitric acid, 

C 6 H 4 (CH 3 ) 2 + 30 = C 6 H 4 (CH 3 )-COOH + H 2 0, 
but the o- and p-acids are best prepared by converting the 



436 CARBOXYLIC ACIDS. 

corresponding toluidines (ra-toluidine cannot easily be ob- 
tained) into the nitriles by Sandra eyer's reaction (p. 384), and 
then hydrolysing with acids or alkalies, 



The o-, m-, and^-toluic acids melt at 103, 110, and 180 
respectively, and resemble benzoic acid very closely, but since 
they contain a methyl-group, they have also properties which 
are not shown by benzoic acid ; on oxidation, for example, 
they are converted into the corresponding phthalic acids, just 
as toluene is transformed into benzoic acid, 



Dicarboxylic Acids. 

The most important dicarboxylic acids are the three 
(o.m.p.) phthalic acids, or benzenedicarboxylic acids, which 
are represented by the formulae, 

COOH COOH 

sCOOH 






COOH k >COOH 

COOH 
Phthalic Acid. Isophthalic Acid. Terephthalic Acid. 

These compounds may be prepared by the oxidation of the 
corresponding dimethylbenzenes with dilute nitric acid, or 
more conveniently by treating the toluic acids with potassium 
permanganate in alkaline solution, 



They are colourless, crystalline substances, and have all the 
ordinary properties of carboxylic acids. They yield normal 
and hydrogen metallic salts, esters, acid chlorides, amides, 
&c., which a. re similarly constituted to, and formed by the 



CARBOXYLIC ACIDS. 437 

same reactions as, those of other dicarboxylic acids (Part I. 
p. 234). 

Phthalic acid, like succinic acid (Part I. p. 240), is con- 
verted into its anhydride when strongly heated, 

O-COOH S ^x-CCX 

> + H 2 0, 
COOH k^^ J CO/ 

but it is very important to notice that an anhydride of iso- 
phthalic acid or of terephthalic acid cannot be produced ; it 
is, in fact, a general rule that the formation of an anhydride 
from one molecule of the acid takes place only when the two 
carboxyl-groups in the benzene nucleus are in the o-position, 
never when they occupy the m- or ^-position. 

When cautiously heated with lime, all these dicarboxylic 
acids yield benzoic acid (p. 430), 



C.H 4 < = C 6 H 6 .COOH + C0 2> 



but if the operation be conducted at a high temperature, 
both carboxyl-groups are displaced by hydrogen, and benzene 
is formed, 



this behaviour clearly shows that these acids are all dicarboxy- 
derivatives of benzene. 

When a trace of phthalic acid is heated with resorcinol 
and a drop of sulphuric acid,* fluorescein (p. 532) is produced, 
and the reddish-brown product, when dissolved in soda 
and poured into a large quantity of water, yields a magnifi- 
cently fluorescent solution. This reaction is shown by all 
the o-dicarboxylic acids of the benzene series, but not by 
the m- and ^-dicarboxylic acids ; it is also shown by acids 
of the fatty series, such as succinic acid, which give internal 

* To convert the acid into its anhydride ; sometimes, as in the case of 
phthalic acid itself, the addition of sulphuric acid is unnecessary. 



438 CARBOXYLIC ACIDS. 

anhydrides that is to say, anhydrides formed from one 
molecule of the acid. 

Phthalic acid, C 6 H 4 (COOH) 2 (benzene-o-dicarboxylic acid), 
may be obtained by oxidising o-xylene or o-toluic acid, but it 
is usually manufactured by oxidising naphthalene (p. 455) 
\vith sulphuric acid in presence of a small quantity of 
mercury ; for laboratory purposes naphthalene tetrachloride, 
C 10 H 8 C1 4 (p. 463), is oxidised with nitric acid. 

Concentrated nitric acid (sp. gr. 1-45, 10 parts) is gradually added 
to naphthalene tetrachloride (1 part), and the mixture heated until 
a clear solution is produced. This is then evaporated to dryness, 
and the residue distilled, the phthalic anhydride (see below), which 
passes over, being reconverted into phthalic acid by boiling it with 
caustic soda ; the acid is then precipitated by adding a mineral 
acid, and the crystalline precipitate purified by recrystallisation 
from boiling water. 

Phthalic acid crystallises in colourless prisms, and melts at 
184, with formation of the anhydride, so that, if the melted 
substance be allowed to solidify, and the melting-point again 
determined, it will be found to be about 128, the melting- 
point of phthalic anhydride. 

Phthalic acid is readily soluble in hot water, alcohol, and 
ether, and gives with metallic hydroxides well-characterised 

salts ; the barium salt, C 6 H 4 <C.^>Ba, obtained as a white 



precipitate by adding barium, chloride to a neutral solution of 
the ammonium salt, is very sparingly soluble in water. 

Ethyl phthalate, C 6 H 4 (COOC 2 H 5 ) 2 , is readily prepared by 
saturating an alcoholic solution of phthalic acid (or its an- 
hydride) with hydrogen chloride. It is a colourless liquid, 
boiling at 295. 

Phthalyl chloride, C 6 H 4 (COC1) 2 , is prepared by heating phthalic 
anhydride (1 mol.) with phosphorus pentachloride (1 mol.). It is a 
colourless oil, boils at 275 (726 mm.), and is slowly decomposed by 
water, with regeneration of phthalic acid. In many of its reactions 
it behaves as if it had the constitution represented by the formula 

CC1 
C 6 H 4 <\ nr 2 ^0 (compare succinyl chloride, Part I. p. 242). 



CARBOXYLIO ACIDS. 439 

CO 
Phthalic anhydride, C 6 H 4 <p~>0, is formed when 

phthalic acid is distilled. It sublimes readily in long needles, 
melts at 128, boils at 284, and is only very gradually de- 
composed by water, but dissolves readily in alkalies, yielding 
salts of phthalic acid. When heated in a stream of ammonia 

CO 

it is converted into phthalimide, CgHxC^^^NH, a sub- 

\j\j 

stance which melts at 229, and yields a potassium derivative, 

CO 

C 6 H 4 <C r , r ,^>NK, on treatment with alcoholic potash. There 
GO 

is thus a great similarity between phthalimide and suc- 
cinimide (Part I. p. 243). 

Potassium phthalimide interacts with various halogen deriva- 
tives, as, for example, with ethyl iodide and with ethylene 
dibromide, giving substituted phthalimides, 



Ethylphthalimide. 

rn 



<CO >N-CH 2 .CH 2 Br + KBr 

Brometliylphthalimide. 



Ethylenediphthalimide. 

These products are hydrolysed by mineral acids and by alkalies 
yielding phthalic acid and an arnine, or a bromo- or hydroxy- 
amine ; ethylphthalimide, for example, gives ethylamine, whereas 
bromethylphthalimide gives bromethylamine, NH 2 -CH 2 -CH 2 Br, or 
amidoethyl alcohol, NH 2 -CH 2 -OH 2 -OH, according to the hydrolys- 
ing agent used. Ethylenediphthalimide yields ethylene diamine, 
NH 2 .CH 2 .CH 2 -NH 2 . 

Isophthalic acid, C 6 H 4 (COOH) 2 (benzene-w-dicarboxylic 
acid), is produced by oxidising m-xylene with nitric acid or 
chromic acid ; or from m-toluic acid (p. 435) by oxidation 
with potassium permanganate in alkaline solution. 



440 CARBOXYLIC ACIDS. 

It crystallises in needles, melts above 300, and when 
strongly heated sublimes unchanged; it is very sparingly 
soluble in water. Methyl isophthalate, C 6 H 4 (COOCH 3 ) 2 , 
melts at 65. 

Terephthalic acid, C 6 H 4 (COOH) 2 (benzene-^-dicarboxylic 
acid), is formed by the oxidation of >-xylene, ^-toluic acid, 
and of all di-alkyl substitution-derivatives of benzene, which, 
like cymene, CH 3 -C 6 H 4 -CH(CH 3 ) 2 , contain the alkyl-groups in 
the ^-position. It is best prepared by oxidising j?-toluic acid 
(p. 435) in alkaline solution with potassium permanganate. 

Terephthalic acid is almost insoluble in water, and, 
when heated, sublimes without melting; the methyl salt, 
C 6 H 4 (COOCH 3 ) 2 , melts at 140. 

Acids, such as isophthalic acid and terephthalic acid, which 
have no definite melting-point, or which melt above 300, are best 
identified by converting them into their methyl salts, which gener- 
ally crystallise well, and melt at comparatively low temperatures. 

For this purpose a centigram of the acid is warmed in a test tube 
with about three times its weight of phosphorus pentachloride, 
and the clear solution, which now contains the chloride of the 
acid, poured into excess of methyl alcohol. As soon as the vigor- 
ous reaction has subsided, the liquid is diluted with water, the 
crude methyl salt collected, recrystallised, and its melting-point 
determined. 

Phenylacetic Acid, Phenylpropionic Acid, and their 
Derivatives. 

Many cases have already been mentioned in which aromatic 
compounds have been found to have certain properties similar 
to those of members of the fatty series, and it has been 
pointed out that this is due to the presence in the former of 
groups of atoms (side-chains) which may be considered as 
fatty radicles ; benzyl chloride, for example, has some pro- 
perties in common with methyl chloride, benzyl alcohol with 
methyl alcohol, benzylamine with methylamine, and so on, 
simply because similar groups or radicles in a similar state 
of combination confer, as a rule, similar properties on the 



CARBOXYLIC ACIDS. 441 

compounds in which they occur. Since, moreover, nearly all 
fatty compounds may theoretically be converted into aromatic 
compounds of the same type by the substitution of a phenyl 
group for hydrogen, it follows that any series of fatty com- 
pounds may have its counterpart in the aromatic group. 
This is well illustrated in the case of the carboxylic acids, 
because, corresponding with the fatty acids, there is a series 
of aromatic acids which may be regarded as derived from 
them in the manner just mentioned. 

Formic acid, H-COOH, 

Benzoic acid, C e H 5 -COOH (phenylformic acid). 
Acetic acid, CHg-COOH, 

Phenylacetic acid, C 6 H 5 .CH 2 -COOH. 
Propionic acid, CH 3 .CH 2 -COOH, 

Phenylpropionic acid, C 6 H 5 -CH 2 .CH 2 .COOH. 
Butyric acid, CH 3 -CH 2 -CH 2 -COOH, 

Phenylbutyric acid, C 6 H 5 .CH 2 -CH 2 .CH 2 .COOH. 

With the exception of benzoic acid, all the above aromatic 
acids are derived from the aromatic hydrocarbons by the sub- 
stitution of carboxyl for hydrogen of the side-chain. They 
have not only the characteristic properties of aromatic com- 
pounds in general, but also those of fatty acids, and, like the 
latter, they may be converted into unsaturated compounds by 
loss of two or more atoms of hydrogen, giving rise to new 
series, as the following example will show. 

Propionic acid, CH 3 -CH 2 -COOH, 

Phenylpropionic acid, C 6 H 5 -CH 2 -CH 2 -COOH. 
Acrylic acid, CH 2 :CH-COOH, 

Phenylacrylic acid, C 6 H 5 .CH:CH.COOH. 
Propiolic acid, CHiC-COOH, 

Phenylpropiolic acid, C 6 H 5 .C;C-COOH. 

Preparation. Aromatic acids, containing the carboxyl- 
group in the side-chain, may be prepared by carefully 
oxidising the corresponding alcohols and aldehydes, and by 
hydrolysing the nitriles with alkalies or mineral acids, 
2H 2 = C 6 H 5 .CH 2 .COOH + NH 3 , 



442 CARBOXYLIC ACIDS. 

but these methods are limited in application, owing to the 
difficulty of obtaining the requisite substances. 

The most important general methods are : (a) By the reduc- 
tion of the corresponding unsaturated acids, compounds which 
are prepared without much difficulty (p. 444), 

C 6 H 5 -CH: CH-COOH + 2H = C 6 H 5 .CH 2 .CH 2 -COOH ; 

and (b) by treating the sodium compound of ethyl malonate 
or of ethyl acetoacetate with the halogen derivatives of the 
aromatic hydrocarbons. As in the latter case the procedure 
is exactly similar to that employed in preparing fatty acids 
(Part I. pp. 193, 198, and 203), one example only need be 
given namely, the synthesis of phenylpropionic acid. 

The sodium compound of ethyl malonate is heated with 
benzyl chloride, and the ethyl benzylmalonate which is thus 
produced, 
C 6 H 5 .CH 2 C1 + CHNa(COOC 2 H 5 ) 2 = 

C 6 H 5 .CH 2 .CH(COOC 2 H 5 ) 2 + NaCl, 

Ethyl Benzylmalonate. 

is hydrolysed with alcoholic potash. The benzylmalonic acid 
is then isolated, and heated at 200, when it is converted into 
phenylpropionic acid, with loss of carbon dioxide, 

C 6 H 5 -CH 2 .CH(COOH) 2 = C 6 H 5 -CH 2 .CH 2 .COOH + C0 2 . 

It should be remembered that only those halogen derivatives 
in which the halogen is in the side-chain can be employed in 
such syntheses, because when the halogen is united with the 
nucleus, as in monochlorotoluene, C 6 H 4 CLCH 3 , for example, 
no action takes place (compare p. 357). 

The properties of two of the most typical acids of this class 
are described below. 

Phenylacetic acid, or a-toluic acid, C 6 H 5 -CH 2 -COOH, is 
prepared by boiling a solution of benzyl chloride (1 mol.) and 
potassium cyanide (1 mol.) in dilute alcohol for about three 
hours ; the benzyl cyanide which is thus formed is purified 
by fractional distillation, and the fraction 220-235 (benzyl 
cyanide boils at 232) is hydrolysed by boiling with dilute 



CARBOXYLIC ACIDS. 443 

sulphuric acid, the product being purified by recrystallisation 
from water, 

C 6 H 5 -CH 2 C1 C 6 H 5 .CH 2 -CN C 6 H 5 -CH 2 .COOH. 
Phenylacetic acid melts at 76-5, boils at 262, and crystallises 
from boiling water in glistening plates ; it has an agreeable, 
characteristic smell, and forms salts and derivatives just as do 
benzoic and acetic acids. 

When oxidised with chromic acid it yields benzoic acid, a 
change very different from that undergone by the isomeric 
toluic acids (p. 436), 

C 6 H 5 .CH 2 .COOH + 30 = C 6 H 6 .COOH + C0 2 + H 2 0. 

Phenylpropionic acid, C 6 H 5 -CH 2 -CH 2 -COOH (hydrocin- 
namic acid), is most conveniently prepared by reducing 
cinnamic acid (see below) with sodium amalgam and water, 

C 6 H 5 .CH:CH.COOH + 2H = C 6 H 5 .CH 2 .CH 2 .COOH, 
but may also be obtained from the product of the action of 
benzyl chloride on the sodium compound of ethyl malonate 
(p. 442). It crystallises from water in needles, melts at 47, 
and distils at 280 without decomposing. 

Cinnamic acid, or phenylacrylic acid, C 6 H 5 -CH:CH-COOH, 
is closely related to phenylpropionic acid, and is one of the 
best-known unsaturated acids of the aromatic series. It 
occurs in large quantities in storax (Styrax offidnalis\ and 
may be obtained from this resin by warming it with caustic 
soda ', the filtered aqueous solution of sodium cinnamate is 
then acidified with hydrochloric acid, and the precipitated 
cinnamic acid purified by recrystallisation from boiling water. 

Cinnamic acid is usually prepared by heating benzaldehyde 
with acetic anhydride and anhydrous sodium acetate, a reaction 
which is most simply expressed by the equation, 

C 6 H 5 -CHO + CH 3 .COONa = C 6 H 5 .CH:CH-COONa + H 2 0. 



A mixture of benzaldehyde (3 parts), acetic anhydride (10 parts), 
and anhydrous sodium acetate (3 parts) is heated to boiling in a 
flask placed in an oil-bath. After about eight hours' time, the 
mixture is poured into water, and distilled in steam to separate 



444 CARBOXYLIC ACIDS. 

the unchanged benzaldehyde ; the residue is then treated with 
caustic soda, the hot alkaline solution filtered from oily and tarry 
impurities, and acidified with hydrochloric acid, the precipitated 
cinnamic acid being purified by recrystallisation from boiling water. 

This method (Perkin's reaction) is a general one for the prepara- 
tion of unsaturated aromatic acids, as by employing the anhydrides 
and sodium salts of other fatty acids, homologues of cinnamic acid 
are obtained. When, for example, benzaldehyde is treated with 
sodium propionate and propioiiic anhydride, phenylmethylacrylic 
acid (a-methylcinnamic acid), C 6 H 5 -CH:C(CH 3 )-COOH, is formed; 
phenylisocrotonic acid, C 6 H 5 -CH:CH-CH 2 -COOH, is not obtained 
by this reaction, because combination always takes place between 
the aldehyde oxygen atom and the hydrogen atoms of that -CH 2 - 
group which is directly united with the carboxyl-radicle of the 
sodium salt. 

Phenylisocrotonic acid may, however, be prepared by heating 
benzaldehyde with a mixture of sodium succinate and succinic 
anhydride, carbon dioxide being eliminated, 
C 6 H 5 -CHO + COOH.CH 2 .CH 2 -COOH = 

C 6 H 5 .CH:CH.CH 2 .COOH + CO 2 + H 2 0. 

It is a colourless, crystalline substance, melts at 86, and boils at 
302 ; at its boiling-point it is gradually converted into a-naphthol 
and water (p. 459). 

Other aldehydes which contain the aldehyde-group directly 
united to the nucleus may be used in the Perkin reaction ; the 
three toluic aldehydes, CH 3 -C 6 H 4 'CHO, for example, give with 
sodium acetate and acetic anhydride the three methylcinnamic 
acids, CH 3 .C 6 H 4 .CH:CH.COOH. 

Cinnamic acid crystallises from water in needles, and melts 
at 133. Its chemical behaviour is in many respects similar 
to that of acrylic acid and other unsaturated fatty acids; 
it combines directly with bromine, for example, yielding 
phenyl-a/3-dibromopropionic acid, C 6 H 5 -CHBr.CHBr.COOH, 
and with hydrogen bromide, giving pJienyl-f$-l>romopropionic 
add, C 6 H 5 -CHBr.CH 2 .COOH. 

A solution of cinnamic acid in sodium carbonate imme- 
diately reduces (decolourises) a dilute solution of potassium 
permanganate at ordinary temperatures ; all unsaturated acids 
show this behaviour, and are thus easily detected (Baeyer). 
On reduction with sodium amalgam and water, cinnamic acid 



CARBOXYLIC ACIDS. 445 

is converted into phenylpropionic acid (p. 443), just as acrylic 
acid is transformed into propionic acid. 

When distilled with lime, cinnamic acid is decomposed into 
carbon dioxide, and plienyletliylene or styrolene,* 

C 6 H 6 -CH:CH.COOH = C 6 H 5 -CH:CH 2 + C0 2 . 
Concentrated nitric acid converts cinnamic acid into a mix- 
ture of about equal quantities of o- and p-nitrocinnamic acids, 
C 6 H 4 (N0 2 )-CH: CH-COOH, which may be separated by convert- 
ing them into their ethyl esters, C 6 H 4 (N0 2 )-CH:CH.COOC 2 H 5 
(by means of alcohol and hydrogen chloride), and recrystallis- 
ing these from alcohol, the sparingly soluble ester of the 
^9-acid being readily separated from the readily soluble ethyl 
0-nitrocinnamate. From the pure esters the acids are then 
regenerated by hydrolysing with dilute sulphuric acid. They 
resemble cinnamic acid closely in properties, and combine 
directly with bromine, yielding the corresponding nitrophenyl- 
dibromopropionic acids, C 6 H 4 (N0 2 )'CHBr-CHBr.COOH. 

Phenylpropiolic acid, C 6 H 5 -C:C-COOH, is obtained by treat- 
ing phenyldibromopropionic acid, or, better, its ethyl ester, with 
alcoholic potash, 

C 6 H 5 .CHBr.CHBr -COOH = C 6 H 5 .C ! C-COOH + 2HBr, 
a method which is exactly similar to that employed in preparing 
acetylene by the action of alcoholic potash on ethylene dibromide. 
It melts at 137, and at higher temperatures, or when heated with 
water at 120, it decomposes into carbon dioxide and phenyl- 
acetijlene, a colourless liquid, which boils at 140, and is closely 
related to acetylene in chemical properties, 

C 6 H 5 .C i C-COOH = C 6 H 5 .C i CH + C0 2 . 

o-Nitrophenylpropiolic acid, C 6 H 4 (NO 2 )-C: C-COOH, maybe simi- 
larly prepared from o-nitrophenyldibromopropionic acid; it is a 
substance of great interest, as when treated with reducing agents, 

* Styrolene, C 6 H 5 -CH:CH 2 , may be taken as a typical example of an 
aromatic hydrocarbon containing an unsaturated side-chain. It is a 
colourless liquid which boils at 145, and in chemical properties shows 
the closest resemblance to ethylene, of which it is the phenyl substitu- 
tion product. With bromine, for example, it yields a dibrom -additive 
product, C 6 H 5 -CHBr-CH 2 Br (dibromethylbenzene), and when heated with 
hydriodic acid, it is reduced to ethylbenzene, C 6 H5-CH 2 -CH 3 . 



446 CARBOXYLIC ACIDS. 

such as hydrogen sulphide, or grape-sugar and potash, it is con- 
verted into indigo-blue (Baeyer), 

2 + 4H = C 16 H 10 N 2 2 + 2C0 2 + 2H 2 O. 

This method of preparation, however, is not of technical value, 
owing to the high price of phenylpropiolic acid (compare p. 540). 



CHAPTER XXX. 

HYDROXYCARBOXYLIG ACIDS. 

The hydroxy-acids of the aromatic series are derived from 
benzoic acid and its homologues, by the substitution of 
hydroxyl-groups for hydrogen atoms, just as glycollic acid, 
for example, is derived from acetic acid (Part I. p. 229) ; like 
the simple hydroxy-derivatives of the hydrocarbons, they may 
be divided into two classes, according as the hydroxyl-group 
is united with carbon of the nucleus or of the side-chain. 
In the first case the hydroxyl-group has the same character 
as in phenols, and consequently hydroxy-acids of this class, 
as, for example, the three (o.m.p.) liydroxy~benzoic acids, 
C 6 H 4 (OH)-COOH, are both phenols and carboxylic acids; in 
the second case, however, the hydroxyl-group has the same 
character as in alcohols, so that the compounds of this class, 
such as mandelic acid, C 6 H 5 -CH(OH)-COOH, have properties 
closely resembling those of the fatty hydroxy-acids ; in other 
words, the differences between the two classes of aromatic 
hydroxy-acids are practically the same as those between 
phenols and alcohols. 

As those acids which contain the hydroxyl-group united 
with carbon of the nucleus form by far the more important 
class, they will be described first, and the following statements 
refer to them only, except where stated to the contrary. 

Preparation. The hydroxy-acids may be prepared from 
the simple carboxylic acids, by reactions exactly similar to 



HYDROXYCARBOXYLIC ACIDS. 447 

those employed in the preparation of phenols from hydro- 
carbons ; that is to say, the acids are converted into nitro- 
compounds, then into amido-compounds, and the latter are 
treated with nitrous acid in the usual manner, 



COOH 



or, the acids are heated with sulphuric acid, and the sulphonic 
acids obtained in this way are fused with potash, 



C 6 H 6 -COOH - C 6 H 4 

It must be borne in mind, however, that as the carboxyl- 
group of the acid determines the position taken up by the 
nitro- and sulphonic-groups (p. 364), only the weta-hydroxy- 
compounds are conveniently prepared in this way directly 
from the carboxylic acids. 

The or^o-hydroxy-acids, and in some cases the meta- and 
para-compounds, are most conveniently prepared from the 
phenols by one of the following methods. 

The dry sodium compound of the phenol is heated at about 
200 in a stream of carbon dioxide, 



2C 6 H 5 .ONa + C0 2 = C 6 H 4 < + C 6 H 5 .OH. 



65 

Under these conditions half the phenol distils over and is re- 
covered ; hut if the sodium compound he first saturated with 
carbon dioxide under pressure, it is converted into an aromatic 
derivative of carbonic acid, which, when heated at about 130 
under pressure, is completely transformed into a salt of the 
hydroxy-acid by intramolecular change, 



C 6 H 5 .ONa + CO, = C 6 H 5 .O.COONa - C 6 H 4 

Sodium Phenylcarbonate. 

Many dihydric and trihydric phenols may be converted 
into the corresponding hydroxy-acids, simply by heating them 
with ammonium carbonate or potassium bicarbonate ; when 



448 HYDROXYCARBOXYLIC ACIDS. 

resorcinol, for example, is treated in this way, it yields a 
mixture of isomeric resorcylic acids, C 6 H 3 (OH) 2 -COOH. 

The second general method of preparing hydroxy-acids 
from phenols consists in "boiling a strongly alkaline solu- 
tion of the phenol with carbon tetrachloride ; the principal 
product is the ortho-acid, but varying proportions of the 
are also formed, 



C 6 H 5 - ONa + CC1 4 + 5NaOH = C 6 H 4 < + 4NaCl + 3H 2 O. 



After the substances have been heated together for some hours, 
the unchanged carbon tetrachloride is distilled off, the residue 
acidified, and the solution extracted with ether ; the crude acid 
obtained on evaporating the ethereal solution is then separated 
from unchanged phenol by dissolving it in sodium carbonate, re- 
precipitated with a mineral acid, and purified by recrystallisation. 

The above method is clearly analogous to Eeimer's reaction 
(p. 421), and the changes which occur during the process may be 
assumed to take place in various stages as indicated below, 

CTT f\TT pi TT ^t-'C'lg pt TT ^C(OH) 3 ~ -p- ^COOH 

6 H 5 .<J] C 6 H 4 < OH - C 6 H 4 < OH C 6 H 4 < OH 

Properties. The hydroxy-acids are colourless, crystalline 
substances, more readily soluble in water and less volatile 
than the acids from which they are derived ; many of them 
undergo decomposition when heated strongly, carbon dioxide 
being evolved ; when heated with lime they are decomposed, 
with formation of phenols, 

C 6 H 4 (OH)-COOH - C 6 H 5 .OH + C0 2 
C 6 H 3 (OH) 2 -COOH - C 6 H 4 (OH) 2 + C0 2 . 

The o-acids, as, for example, salicylic acid, give, in neutral 
solution, a violet colouration with ferric chloride, whereas the 
ra- and >-hydroxy-acids, such as the m- and ^>-hydroxybenzoic 
acids, give no colouration. 

The chemical properties of the hydroxy-acids will be readily 
understood when it is remembered that they are both phenols 
and carboxylic acids. As carboxylic acids they form salts by 
the displacement of the hydrogen atom of the carboxyl-group, 



HYDROXYCARBOXYLTC ACIDS. 449 

such salts being obtained on treating with carbonates or with 
the calculated quantity of the metallic hydroxide ; when, 
however, excess of alkali hydroxide is employed, the hydrogen 
of the phenolic hydroxyl-group is also displaced, just as in 
phenol itself. It is clear, therefore, that hydroxy-acids 
form both mono- and di-metallic salts ; salicylic acid, for 
example, yielding the two sodium salts, C 6 H 4 (OH)-COONa 
and C 6 H 4 (ONa).COONa. 

The di-metallic salts are decomposed by carbonic acid, 
with formation of mono-metallic salts, just as the phenates 
are resolved into the phenols ; the metal in combination 
with the carboxyl-group, however, cannot be displaced in 
this way. 

The esters of the hydroxy-acids are prepared in the 
usual manner namely, by saturating a solution of the acid 
in the alcohol with hydrogen chloride (Part I. p. 191); by 
this treatment the hydrogen of the carboxyl-group only 
is displaced, ordinary esters, such as methyl 'salicylate, 
C 6 H 4 (OH)-COOCH 3 , being formed; these compounds have 
still phenolic properties, and dissolve in caustic alkalies, form- 
ing metallic derivatives, such as methyl potassiosalwylate, 
C 6 H 4 (OK)-COOCH 3 , which, when heated with alkyl halogen 
compounds, yield alkyl-derivatives, such as methyl methyl- 
salicylate, C 6 H 4 (OCH 3 )-COOCH 3 . On hydrolysing di-alkyl 
compounds of this kind with alcoholic potash, only the alkyl 
of the carboxyl-group is removed, methyl methylsalicylate, 
for example, yielding the potassium salt of methylsalicylic 
acid, 



The other alkyl-group is not eliminated even on boiling 
with alkalies, a behaviour which corresponds with that of 
the alkyl-group in derivatives of phenols, such as anisole, 
C 6 H 5 -OCH 3 (p. 405) ; just, however, as anisole is decomposed 
into phenol and methyl iodide when heated with hydriodic 

Org. Chein. 2 C 



450 HYDROXYCARBOXYLIG ACIDS. 

acid, so methylsalicylic acid under similar conditions yields the 
hydroxy-acid, 

,COOH ,COOH 

6 H 4\QQ H +J: 6 H 4\OH 3 

Salicylic acid, or o-hydroxybenzoic acid, C 6 H 4 (OH)-COOH, 
occurs in the blossom of Spiraea ulmaria, and is also found 
in considerable quantities, as methyl salicylate, in oil of 
wintergreen (Gaultlieria procumbens). It used to be pre- 
pared, especially for pharmaceutical purposes, by hydrolysing 
this oil with potash ; after boiling off the methyl alcohol 
(Part I. p. 89), the solution is acidified with dilute sul- 
phuric acid, and the precipitated salicylic acid purified by 
recrystallisation from water. 

Salicylic acid may be obtained by oxidising salicylalde- 
hyde (p. 422), or salicylic alcohol (saligenin, p. 416), with 
chromic acid, by treating o-amidobenzoic acid (anthranilic 
acid, p. 435) with nitrous acid, and also by boiling phenol 
with caustic soda and carbon tetrachloride. 

It is now prepared on the large scale by treating sodium 
phenate with carbon dioxide under pressure, and then heating 
the sodium, phenylcarbonate, C 6 H 5 -OCOONa, which is thus 
formed, at 120-140 under pressure, when it undergoes intra- 
molecular change into sodium salicylate (p. 447). 

Salicylic acid is sparingly soluble in cold (1 in 400 parts at 
15), but readily in hot, water, from which it crystallises in 
needles, melting at 156 ; its neutral solutions give with ferric 
chloride an intense violet colouration. When rapidly heated 
it sublimes, and only slight decomposition occurs ; but when 
distilled slowly, a large proportion decomposes into phenol 
and carbon dioxide, this change being complete if the acid be 
distilled with lime. 

Salicylic acid is a powerful antiseptic, and, as it has no 
smell, it is frequently used as a disinfectant instead of 
phenol; it is also extensively employed in medicine and as a 
food preservative. The mono-metallic salts of salicylic acid, 
as, for example, potassium salicylate, C 6 H 4 (OH)-COOK, and 



HYDROXYCARBOXYLIC ACIDS. 451 

calcium salicylate, {C 6 H 4 (OH)-COO} 2 Ca, are prepared by 
neutralising a hot aqueous solution of the acid with metallic 
carbonates ; they are, as a rule, soluble in water. The di- 

metallic salts, such as C 6 H 4 (OK)-COOK and C 6 



are obtained in a similar manner, employing excess of the 
metallic hydroxides ; with the exception of the salts of the 
alkali metals, these di-metallic compounds are insoluble ; they 
are all decomposed by carbonic acid, with formation of the 
mono-metallic salts, 



+ C0 2 + H 2 = 2C 6 H 4 < + K 2 C0 3 . 

Methyl salicylate, C 6 H 4 (OH)-COOCH 3 , prepared in the 
manner described (p. 449), or by distilling a mixture of salicylic 
acid, methyl alcohol, and sulphuric acid (Part I. p. 191), is 
an agreeably-smelling oil, boiling at 224; ethyl salicylate, 
C 6 H 4 (OH)-COOC 2 H 5 , boils at 223. 

Methyl methylsalicylate, C 6 H 4 (OCH 3 )-COOCH 3 , is formed when 
methyl salicylate is heated with methyl iodide and potash (1 mol.) 
in alcoholic solution ; it is an oil boiling at 228. 

Methylsalicylic acid, C 6 H 4 (OCH 3 ) COOH, is obtained when its 
methyl salt is hydrolysed with potash ; it is a crystalline substance, 
melting at 98-5, and when heated with hydriodic acid it is decom- 
posed, giving salicylic acid and methyl iodide ; the other halogen 
acids have a similar action. 

m-Hydroxybenzoic acid is prepared by fusing w-sulphobenzoic 
acid with potash, and also by the action of nitrous acid on 
m-amidobenzoic acid. It melts at 200, does not give a coloura- 
tion with ferric chloride, and when distilled with lime it is 
decomposed into phenol and carbon dioxide. 

p-Hydroxybenzoic acid is formed, together with salicylic acid, by 
the action of carbon tetrachloride and soda on phenol ; it may also 
be obtained from^-sulphobenzoic acid by fusing with potash, or by_ 
the action of nitrous acid on jo-amidobenzoic acid. 

It is prepared by heating potassium phenate in a stream of carbon 
dioxide at 220 as long as phenol distils over; if, however, the 
temperature be kept below 150, potassium salicylate is formed. 
The residue is dissolved in water, the acid precipitated from the 
filtered solution by adding hydrochloric acid, and purified by 



452 HYDROXYCARBOXYLIC ACIDS. 

recrystallisation from water. ^-Hydroxybenzoic acid melts at 
210, and is completely decomposed on distillation into phenol and 
carbon dioxide; its aqueous solution gives no colouration with 
ferric chloride. 

Anisic acid, >-methoxybenzoic acid, C 6 H 4 (OCH 3 )-COOH, 
is obtained by oxidising anethole, C 6 H 4 (OCH 3 ).CH:CH-CH 3 
(the principal constituent of oil of aniseed) with chromic 
acid, when the group -CH:CH-CH 3 is converted into -COOH ; 
it may also be prepared from j)-hydroxybenzoic acid by 
means of reactions analogous to those employed in the for- 
mation of methylsalicylic acid from salicylic acid (p. 451). 

Anisic acid melts at 185, and when distilled with lime 
it is decomposed, with formation of anisole (p. 405) ; when 
heated with fuming hydriodic acid, it yields jp-hydroxy ben zoic 
acid and methyl iodide. 

There are six dihydroxybenzoic acids, C 6 H 3 (OH) 2 -COOH, 
two of which are derived from catechol, three from resorcinol, 
and one from hydroquinone ; the most important of these is 
protocateclmic acid, [OH:OH:COOH = 1:2:4], one of the two 
isomeric catecholcarboxylic acids. This compound is formed 
on fusing many resins, such as catechu and gum benzoin, and 
also certain alkaloids, with potash, and it may be prepared 
synthetically by heating catechol with water and ammonium 
carbonate at 140. 

It crystallises from water, in which it is very soluble, in 
needles, melts at 199, and when strongly heated it is decom- 
posed into catechol and carbon dioxide ; its aqueous solution 
gives with ferric chloride a green solution, which becomes 
violet and then red on the addition of sodium bicarbonate. 

Gallic acid, or pyrogallolcarboxylic acid, 

C 6 H 2 (OH) 3 .COOH,[OH:OH:OH:COOH = 1:2:3:5], 
is a trihydroxybenzoic acid ; it occurs in gall-nuts, tea, and 
many other vegetable products, and is best prepared by boil- 
ing tannin (see below) with dilute acids. It crystallises in 
needles, and melts at 220, being at the same time resolved 
into pyrogallol (p. 412) and carbon dioxide; it is readily 



HYDROXYCARBOXYLIC ACIDS. 453 

soluble in water, and its aqueous solution gives with ferric 
chloride a bluish-black precipitate. Gallic acid is a strong 
reducing agent, and precipitates gold, silver, and platinum 
from solutions of their salts. 

Tannin, digallic acid, or tannic acid, C 14 H 10 9 , occurs in 
large quantities in gall-nuts, and in all kinds of bark, from 
which it may be extracted with boiling water. It is an 
almost colourless, amorphous substance, and is readily soluble 
in water; its solutions possess a very astringent taste, and 
give with ferric chloride an intense dark-blue solution, for 
which reason tannin is largely used in the manufacture of 
inks. 

When boiled with dilute sulphuric acid, tannin is com- 
pletely converted into gallic acid, a fact which shows that it 
is the anhydride of this acid, 



Tannin is used largely in dyeing as a mordant, owing to its 
property of forming insoluble coloured compounds with many 
dyes. It is also extensively employed in ' tanning ; ' when 
animal skin or membrane, after suitable preliminary opera- 
tions, is placed in a solution of tannin, or in contact with 
moist bark containing tannin, it absorbs and combines with 
the tannin, and is converted into a much tougher material ; 
such tanned skins constitute leather. 

Mandelic acid, C 6 H 5 -CH(OH).COOH (phenylglycollic 
acid), is an example of an aromatic hydroxy-acid containing 
the hydroxyl-group in the side-chain. It may be obtained 
by boiling amygdalin (which yields benzaldehyde, hydrogen 
cyanide, and glucose, p. 418) with hydrochloric acid, but it 
is usually prepared by treating benzaldehyde with hydrocyanic 
acid and hydrolysing the resulting hydroxy cyanide, a method 
analogous to that employed in the synthesis of lactic acid from 
aldehyde (Part I. p. 234), 

C 6 H 5 .CHO + HCN = C 6 H 5 .CH(OH>CN 
C e H 5 .CH(OH).CN + 2H 2 = C 6 H 5 -CH(OH).COOH + NH 3 . 



454 HYDROXYCARBOXYLIC ACIDS. 

Mandelic acid melts at 133, is moderately soluble in water, 
and shows in many respects the greatest resemblance to lactic 
acid (methylglycollic acid) ; when heated with hydriodic acid, 
for example, it is reduced to phenylacetic acid (p. 442), just 
as lactic acid is reduced to propionic acid (Part I. p. 232), 
C 6 H 5 .CH(OH).COOH + 2HI = C 6 H 5 .CH 2 .COOH + 1 2 + H 2 0. 
The character of the hydroxyl-group in mandelic acid is, in 
fact, quite similar to that of the hydroxyl-group in the fatty 
hydroxy-acids and in the alcohols, so that there are many 
points of difference between mandelic acid and acids, such as 
salicylic acid, which contain the hydroxyl-group united with 
carbon of the nucleus ; when, for example, ethyl mandelate, 
C 6 H 5 .CH(OH)-COOC 2 H 5 , is treated with caustic alkalies, it 
does not yield an alkali derivative, although the hydrogen of 
the hydroxyl-group is displaced on treating with sodium or 
potassium. 

Mandelic acid, like lactic acid, exists in three optically 
different forms. The synthetical acid is optically inactive, 
but the acid prepared from amygdalin is levo-rotatory. 



CHAPTER XXXI. 

NAPHTHALENE AND ITS DERIVATIVES. 

All the aromatic hydrocarbons hitherto described, with 
the exception of diphenyl, diphenylmethane, and triphenyl- 
methane (p. 350), contain only one closed-chain of six 
carbon atoms, and are very closely and directly related to 
benzene; most of them may be prepared from benzene 
by comparatively simple reactions, and reconverted into 
this hydrocarbon, perhaps even more readily, so that they 
may all be classed as simple benzene derivatives. The 
exceptions just mentioned are also, strictly speaking, 



NAPHTHALENE AND ITS DERIVATIVES. 455 

derivatives of benzene, although at the same time they 
may be regarded as hydrocarbons of quite another class, 
since diphenyl and dipheny 1m ethane contain two, and tri- 
phenylm ethane three, closed-chains of six carbon atoms. 
There are, in fact, numerous classes or types of aromatic 
hydrocarbons, and, just as benzene is the parent substance 
of a vast number of derivatives, so also these other hydro- 
carbons form the starting-points of new homologous series 
and of derivatives of a different type. 

The hydrocarbons naphthalene and anthracene, which are 
now to be described, are perhaps second only to benzene 
in importance ; each forms the starting-point of a great 
number of compounds, many of which are extensively 
employed in the manufacture of dyes. 

Naphthalene, C 10 H 8 , occurs in coal-tar in larger quantities 
than any other hydrocarbon, and is easily isolated from this 
source in a pure condition ; the crystals of crude naphthalene, 
which are deposited on cooling from the fraction of coal-tar 
passing over between 170 and 230 (p. 307), are first pressed 
to get rid of liquid impurities, and then warmed with a 
small quantity of concentrated sulphuric acid, which con- 
verts most of the foreign substances into non-volatile 
sulphonic acids ; the naphthalene is then distilled in steam, 
or sublimed, and is thus obtained almost chemically pure. 

Naphthalene crystallises in large, lustrous plates, melts 
at 79, and boils at 218. It has a highly characteristic 
smell, and is extraordinarily volatile, considering its high 
molecular weight so much so, in fact, that only part of 
the naphthalene in crude coal-gas is deposited in the con- 
densers (p. 305), the rest being carried forward into the 
purifiers, and even into the gas-mains, in which it is 
deposited in crystals in cold weather, principally at the 
bends of the pipes, frequently causing stoppages. It is 
insoluble in water, but dissolves freely in hot alcohol and 
ether, from either of which it may be crystallised. Like 
many other aromatic hydrocarbons, it combines with picric 



456 NAPHTHALENE AND ITS DERIVATIVES. 

acid, when the two substances are dissolved together in 
alcohol, forming naphthalene picrate, a yellow crystalline 
compound of the composition, 

C 10 H 8 ,C 6 H 2 (N0 2 ) 3 .OH, 

which melts at 149. 

As the vapour of naphthalene burns with a highly luminous 
flame, the hydrocarbon is used to some extent for carburet- 
ting coal-gas that is to say, for increasing its illuminating 
power ; for this purpose the gas is passed through a vessel 
which contains coarsely-powdered naphthalene, gently heated 
by the gas flame, so that the hydrocarbon volatilises and 
burns with the gas. The principal use of naphthalene, 
however, is for the manufacture of a number of derivatives 
which are employed in the colour industry. 

Constitution. Naphthalene has the characteristic properties 
of an aromatic compound that is to say, its behaviour 
under various conditions is similar to that of benzene and 
its derivatives, and different from that of fatty compounds ; 
when treated with nitric acid, for example, it yields nitro- 
derivatives, and with sulphuric acid it gives sulphonic acids. 
This similarity between benzene and naphthalene at once 
suggests a resemblance in constitution, a view which is 
confirmed by the fact that naphthalene, like benzene, is 
a very stable compound, and is resolved into simpler sub- 
stances only with difficulty. When, however, naphthalene 
is boiled with dilute nitric or chromic acid, or heated 
with sulphuric acid (p. 438), it is slowly oxidised, yielding 
carbon dioxide and (o?^^o)-phthalic acid, C 6 H 4 (COOH) 2 . 

Now the formation of phthalic acid in this way is a 
fact of very great importance, since it is a proof that 
naphthalene contains the group, 



or 




NAPHTHALENE AND ITS DERIVATIVES. 457 

that is to say, that it contains a benzene nucleus to which 
two carbon atoms are united in the or^o-position to one 
another. This fact alone, however, is insufficient to establish 
the constitution of the hydrocarbon, since there are still two 
carbon and four hydrogen atoms to be accounted for, and 

there are many different ways in which these might be 

n 
united with the C 6 H 4 < C group. 

Clearly, therefore, it is important to ascertain the structure 
of that part of the naphthalene molecule which has been 
oxidised to carbon dioxide and water to obtain, if possible, 
some decomposition product of known constitution in which 
these carbon and hydrogen atoms are retained in their 
original state of combination. 

Now this can be done in the following way : When nitro- 
naphthalene, C 10 H 7 -N0 2 , a simple mono-substitution product 
of the hydrocarbon, is boiled with dilute nitric acid, it yields 
nitrophthalic acid, C 6 H 3 (N0 2 )(COOH) 2 ; therefore, again, 
naphthalene contains a benzene nucleus, and the nitro- 
group in nitronaphthalene is combined with this nucleus. 
If, however, the same nitronaphthalene be reduced to amido- 
naphthalene, C 10 H 7 -NH 2 , and the latter oxidised, phthalic 
acid (and not amidophthalic acid) is obtained; this last 
fact can only be explained by assuming, either that the 
benzene nucleus, which is known to be united with the 
amido-group, has been destroyed, or that the amido-group 
has been displaced by hydrogen during oxidation. Since, 
however, the latter alternative is contrary to all experience, 
the former must be accepted, and it must be concluded 
that the benzene nucleus, which is contained in the oxida- 
tion product of amidonaphthalene, is not the same as that 
present in the oxidation product of nitronaphthalene ; in 
other words, different parts of the naphthalene molecule 

have been oxidised to carbon dioxide and water in the 

n 
two cases, and yet in both the group C 6 H 4 <Cp remains. 



458 



NAPHTHALENE AND ITS DERIVATIVES. 



The constitution of naphthalene must therefore be expressed 
by the formula, 



CH 



CH 




CH 



CH 



This will be evident if the above changes be represented 
with the aid of this formula. When nitroriaphthalene is 
oxidised, the nucleus B (see below), which does not contain 
the nitro-group, is destroyed, as indicated by the dotted 
lines, the product being nitrophthalic acid ; when, on the 
other hand, amidonaphthalene is oxidised, the nucleus A, 
combined with the amido-group, is attacked in preference 
to the other, and phthalic acid is formed, 



NO 




Naphthalene. 



NH 2 




Nitrouaphthalene. 



COOH 



COOH 
Nitrophthalic Acid. 




Amidonaphthalene. 



COOH' 

Phthalic Acid. 



The constitution of naphthalene was first established in 
this way by Graebe in 1880, although the above formula 
had been suggested by Erlenmeyer as early as 1866; that 
the hydrocarbon is composed of two closed-chains of six 
carbon atoms condensed* together in the o-position, as 
shown above, has since been confirmed by syntheses of 

* The term condensed used in this and in similar cases signifies that 
certain carbon atoms are contained in, or are common to, both nuclei. 



NAPHTHALENE AND ITS DERIVATIVES. 459 

its derivatives, but even more conclusively by the study 
of the isomerism of its substitution products. 

The difficulty of determining and of expressing the actual state 
or disposition of the fourth affinity of each of the carbon atoms 
in naphthalene is just as great as in the case of benzene. If the 
carbon atoms be represented as united by alternate double Unkings, 
as in the formula on the left-hand side (see below), there is the 
objection that they do not show, as indicated, the behaviour of 
carbon atoms in fatty unsaturated compounds, as explained more 
fully in the case of benzene. For this reason the formula on the 
right-hand side (see below) has been suggested as perhaps prefer- 
able, the lines drawn towards the centres of the nuclei having 
the same significance as in the centric formula for benzene (p. 317). 
The simple, double-hexagon formula given above is usually em- 
ployed for the sake of convenience. 





Naphthalene may be obtained synthetically by passing 
the vapour of phenylbutylene, C 6 H 5 .CH 2 -CH 2 .CH:CH 2 * (or 
of phenylbutylene dibromide, C 6 H 5 -CH 2 -CH 2 .CHBr-CH 2 Br), 
over red-hot lime, the change involving loss of hydrogen, 
as in the formation of other aromatic from fatty hydrocarbons 
(p. 310), 

/CH:CH 

C 6 H 5 .CH 2 .CH 2 .CH:CH 2 -C 6 H 4 < | +2H 2 . 

X CH:CH 

A most important synthesis of naphthalene was accom- 
plished by Fittig, who showed that a-naphthol (a-hydroxy- 
naphthalene) is formed on boiling phenylisocrotonic acid 
(p. 444) with water. This change probably takes place 
in two stages, the first product being a keto-derivative of 

* Phenylbutylene is obtained by treating a mixture of benzyl chloride 
and allyl iodide with sodium, 

C 6 H 3 -CH 2 C1 + CH 2 I-CH:CH 2 + 2Na= C 6 H 5 -CH 2 -CH 2 -CH:CH2 + NaCl + Nal. 
It is a liquid, boiling at 178, and, like butylene, it combines directly with 
one molecule of bromine, yielding the dibromide. 



460 



NAPHTHALENE AND ITS DERIVATIVES. 



naphthalene, which passes into a-naphthol by intramolecular 
change (compare Part I. p. 200), 



CH 



CH 




C(OH) 

The a-naphthol thus obtained may be converted into 
naphthalene by distillation with zinc-dust, just as phenol 
may be transformed into benzene (p. 341). 

Isomerism of Naphthalene Derivatives. As in the case 
of benzene, the study of the isomerisrn of the substitu- 
tion products affords the most convincing evidence that the 
accepted constitutional formula of naphthalene is correct. 
In the first place, naphthalene differs from benzene in 
yielding two isomeric mono-substitution products ; there 
are, for example, two monochloronaphthalenes, two mono- 
hydroxynaphthalenes, two mononitronaphthalenes, &c. This 
fact is readily accounted for; on considering the constitu- 
tional formula of naphthalene, which may be conveniently 
written, 



or 



numbered or lettered as shown (the symbols C and H being 
omitted for the sake of simplicity), it will be evident that 
the eight hydrogen atoms are not all similarly situated 
relatively to the rest of the molecule. If, for example, 
the hydrogen atom (1) were displaced by chlorine or 
hydroxyl, the substitution product would be isomeric, but 
not identical with that produced by the displacement of 





NAPHTHALENE AND ITS DERIVATIVES. 461 

the hydrogen atom (2). In the first case the substituting 
atom or group would be united with a carbon atom which 
is itself directly united with a carbon atom common to 
both nuclei, whereas in the other case this would not be 
so. Clearly, then, the fact that the mono-substitution 
products of naphthalene exist in two isomeric forms is in 
accordance with the above constitutional formula. Further, 
it will be seen that no more than two such isomerides 
could be obtained, because the positions 1.4.1 'A' (the four 
a-positions) are identical, and so also are the positions 2. 3. 2'. 3' 
(the four /^-positions) ; the isomeric mono-substitution pro- 
ducts are, therefore, usually distinguished by using the letters 
a and p. 

When two hydrogen atoms in naphthalene are displaced by 
two identical groups or atoms, ten isomeric di-derivatives may 
be obtained. Denoting the positions of the substituents by 
the system of numbering already used, these isomerides 
would be, 

1:2, 1:3, 1:4, 1:4', 1:3', 1:2', 1:1', 2:3, 2:3', 2:2', 

all other possible positions being identical with one of these ; 
2:4', for example, is the same as 1:3', 2':4 and 3:1', and l':4 is 
identical with 1:4'. The constitution of such a di-derivative 
is usually expressed with the aid of numbers in this manner, 
as it is necessary to show whether the substituents are 
combined with the same or with different nuclei. 

When the two atoms or groups are present in one and 
the same nucleus, their relative position is similar to that of 
groups in the o-, m-, or j9-position in benzene. The positions 
1:2, 2:3, and 3:4 correspond with the ortho-, 1:3 and 2:4 
with the meta-, and 1:4 with the jpara-position, and simi- 
larly in the case of the other nucleus. The position 1:1' or 
4:4', however, is different from any of these, and is termed 
the peri-position ; groups thus situated behave in much the 
same way as those in the o-position in the benzene and 
naphthalene nuclei. 



462 NAPHTHALENE AND ITS DERIVATIVES. 

Derivatives of Naphthalene. 

The homologues of naphthalene that is to say, its alkyl 
substitution products, are of comparatively little importance, 
but it may be mentioned that they may be prepared from the 
parent hydrocarbon by methods similar to those employed in 
the case of the corresponding benzene derivatives, as, for 
example, by treating naphthalene with alkyl halogen com- 
pounds and aluminium chloride, 

^10^8 + C 2 H 5 I = C 10 H 7 -C 2 H 5 + HI, 

and by treating the bromonaphthalenes with an alkyl halogen 
compound and sodium, 

C l0 H 7 Br + CH 3 Br + 2Na = C 10 H r CH 8 + 2NaBr. 

a-Methylnaphthalene, C 10 H 7 -CH 8 , is a colourless liquid, 
boiling at 240-242, but p-methylnaplithalene is a solid, 
melts at 32, and boils at 242; both these hydrocarbons 
occur in coal-tar. 

The halogen mono-substitution products of naphthalene are 
also of little importance. They may be obtained by treating 
the hydrocarbon, at its boiling-point, with the halogens 
(chlorine and bromine), but only the a-derivatives are formed 
in this way. Both the a- and the /^-compounds may be 
obtained by treating the corresponding naphthols (p. 466), 
or, better, the naphthalenesulphonic acids (p. 467) with 
pentachloride or pentabromide of phosphorus, 

C 10 H r S0 2 Cl + PC1 5 = C 10 H 7 C1 + POC1 3 + SOC1 2 , 
or by converting the naphthylamines (p. 465) into the corre- 
sponding diazo-compounds, and decomposing the latter with a 
halogen cuprous salt (pp. 383-384), 

C 10 H r ]m 2 -i C 10 H 7 .K 2 C1 C 10 H 7 C1. 

All these methods correspond with those described in the 
case of the halogen derivatives of benzene, and are carried out 
practically in a similar manner. 

a-Chloronaphthalene, C 10 H 7 C1, is a liquid, boiling at about 



NAPHTHALENE AND ITS DERIVATIVES. 463 

263, but the ^-derivative is a crystalline substance, melting 
at 56, and boiling at 265. 

a-Bromonaphthalene, C^H^Er, is also a liquid at ordinary 
temperatures, and boils at 279, but the 13-derivative is 
crystalline, and melts at 59. 

The chemical properties of these, and of other halogen 
derivatives of naphthalene, are similar to those of the halogen 
derivatives of benzene; the halogen atoms are very firmly 
combined, and are not displaced by hydroxyl-groups on 
boiling with alkalies, &c. 

Naphthalene tetrachloride, C 10 H 8 C1 4 , is an important halo- 
gen additive product, which is produced on passing chlorine 
into a vessel containing coarsely-powdered naphthalene, at 
ordinary temperatures. It forms large colourless crystals, 
melts at 182, and is converted into dichloronaphthalene, 
C 10 H 6 C1 2 (a substitution product of naphthalene), when 
heated with alcoholic potash ; it is readily oxidised by nitric 
acid, yielding phthalic and oxalic acids, a fact which shows 
that all the chlorine atoms are present in one and the same 
nucleus ; the constitution of the compound is therefore 

. _, _ .CHCLCHCk 
expressed by the iormula ^e^^Tri P 



The formation of this additive product shows that naphthalene, 
like benzene, is not really a saturated compound, although it 
usually behaves as such ; many other compounds, formed by the 
addition of four atoms of hydrogen to naphthalene, or to a naphtha- 
lene derivative, are known, and it has been found that when one 
of the nuclei is thus fully reduced, the atoms or groups directly 
united to it acquire the character which they have in fatty com- 
pounds, whereas those united to the unreduced nucleus retain the 
character which they have in simple substitution products of 
benzene. The amido-group in the tetrahydro-^-naphthylamine of 



x 2 . 

the constitution C fi EL< | , for example, has the same 

X CH 2 .CH 2 
character as that in fatty amines, whereas in the case of the 

/CH^-CHa 

isomeric tetrahydro-p-naphthylamine, NHa-CeHg^ I , the 

^CH^-CELj 



464 NAPHTHALENE AND ITS DERIVATIVES. 

amido-group has the same properties as that in aniline, because 
it is combined with the unreduced nucleus. Such tetrahydro- 
derivatives of naphthalene are termed aromatic (ar.-) or ali- 
cyclic (ac.-)> according as the substituent is contained in the 
unreduced or in the reduced nucleus. 

Nitro-derivatives. Naphthalene, like benzene, is readily 
acted on by concentrated nitric acid, yielding nitro-deriva- 
tives, one, two, or more atoms of hydrogen being displaced 
according to the concentration of the acid and the tem- 
perature at which the reaction is carried out; the presence 
of sulphuric acid facilitates nitration for reasons already men- 
tioned. The chemical properties of the nitro-naphthalenes are 
in nearly all respects similar to those of the nitro-benzenes. 

a-Nitronaphthalene, C 10 H r -N0 2 , is best prepared in small 
quantities by dissolving naphthalene in acetic acid, adding 
concentrated nitric acid, and then heating on a water-bath 
for half-an-hour ; the product is poured into water, and the 
nitronaphthalene purified by recrystallisation from alcohol. 
On the large scale it is prepared by treating naphthalene with 
nitric and sulphuric acids, the method being similar to that 
employed in the case of nitrobenzene (p. 365). It crystallises 
in yellow prisms, melts at 61, and boils at 304; on oxidation 
with nitric acid it yields nitrophthalic acid (p. 458). 

^-Nitronaphthalene is not formed on nitrating naphthalene, 
but it may be prepared by dissolving /3-nitro-a-naphthylamine 
(a compound obtained on treating a-naphthylamine with dilute 
nitric acid) in an alcoholic solution of hydrogen chloride, 
adding finely-divided sodium nitrite, and then heating the 
solution of the diazo-compound (compare p. 383), 
C 10 H 6 (N0 2 >N 2 C1 + C 2 H 5 .OH = 

C 10 H r N0 2 + N 2 + HC1 + C 2 H 4 0. 
It crystallises in yellow needles, melting at 79. 

The amido-derivatives of naphthalene are very similar in 
properties to the corresponding benzene derivatives, except 
that even the monamido-compounds are crystalline solids ; they 
have a neutral reaction to litmus, and yet are distinctly basic 



NAPHTHALENE AND ITS DERIVATIVES. 465 

in character, since they neutralise acids, forming salts, which, 
however, are decomposed by the hydroxides and carbonates 
of the alkalies. These amido-compounds, moreover, may be 
converted into diazo-compounds, amidoazo-compounds, &c., 
by reactions similar to those employed in the case of the 
amido-benzenes, and many of the substances obtained in this 
way, as well as the amido-compounds themselves, are exten- 
sively employed in the manufacture of dyes. 

a-Naphthylamine, C 10 H 7 -NH 2 , may be obtained by heating 
a-naphthol with ammonio-zinc chloride or ammonio-calcium 
chloride at 250,* 

C 10 H 7 .OH + NH 3 = C 10 H r NH 2 + H 2 0, 

but it is best prepared by reducing a-nitronaphthalene with 
iron-filings and acetic acid, 

C 10 H 7 .N0 2 + 6H = C 10 H 7 -NH 2 + 2H 2 0. 

It is a colourless, crystalline substance, melting at 50, and 
boiling at 300; it has a disagreeable smell, turns red on 
exposure to the air, and its salts give a blue precipitate with 
ferric chloride and other oxidising agents. On oxidation 
with a boiling solution of chromic acid, it is converted into 
a-naphthaquinone (p. 468). 

/3-Naphthylamine is not prepared from /3-nitronaphthalene 
(as this substance is itself only obtained with difficulty), but 
from /3-naphthol, as described in the case of the a-compound. 
It crystallises in colourless plates, melts at 112, and boils at 
294 ; it differs markedly from a-naphthylamine in being 
odourless, and its salts give no colouration with ferric 
chloride. On oxidation with potassium permanganate, it 
yields phthalic acid. 

* Prepared by passing ammonia over anhydrous zinc or calcium chloride. 
These compounds decompose when heated, evolving ammonia, and are, 
therefore, conveniently employed in many reactions requiring the presence 
of ammonia at high temperatures ; the zinc or calcium chloride resulting 
from their decomposition also favours the reaction in those cases in which 
water is formed, as both substances are powerful dehydrating agents. 
Ammonium acetate may be employed for a similar purpose, as it dissociates 
at comparatively low temperatures, but its action is less energetic. 

Org. Chem. 2 D 



466 NAPHTHALENE AND ITS DERIVATIVES. 

The two naphthols, or monohydroxy-derivatives of naph- 
thalene, correspond with the monohydric phenols, and are 
compounds of considerable importance, as they are exten- 
sively employed in the colour industry. They both occur 
in coal-tar, but only in small quantities, and are, therefore, 
prepared either by diazotising the corresponding naphthyl- 
amines, 

C 10 H r NH 2 C 10 H 7 -N 2 C1 C 10 H r OH, 

or by fusing the corresponding sulphonic acids with potash 
(compare p. 400), 

C 10 H r -S0 3 K + KOH = C 10 H r OH + K 2 S0 8 . 

Their properties are, on the whole, very similar to those of 
the phenols, and, like the latter, they dissolve in caustic 
alkalies, yielding metallic derivatives, which are decomposed 
by carbonic acid ; the hydrogen of the hydroxyl-group in 
the naphthols may also be displaced by an acetyl-group or 
by an alkyl-group, just as in phenols, and on treatment with 
pentachloride or pentabromide of phosphorus, a halogen atom 
is substituted for the hydroxyl-group. The naphthols further 
resemble the phenols in giving colour reactions with ferric 
chloride. 

In a few respects, however, there are certain differences between 
the chemical properties of the naphthols and phenols, inasmuch as 
the hydroxyl-groups in the former more readily undergo change ; 
when, for example, a naphthol is heated with ammonio-zinc chloride 
at 250, it is converted into the corresponding amido-compound (see 
above), whereas the conversion of phenol into aniline requires a 
temperature of 300-350, other conditions remaining the same. 
Again, when a naphthol is heated with an alcohol and hydrogen 
chloride, it is converted into an alkyl-derivative, whereas alkyl- 
derivatives of phenols cannot, as a rule, be obtained in this way. 
In some respects the naphthols form, as it were, a connecting-link 
between the phenols and the alcohols. 

a-Naphthol, C 10 H 7 -OH, is formed, as previously stated 
(p. 459), on boiling phenylisocrotonic acid with water, an 
important synthesis, which proves that the hydroxyl-group is 



NAPHTHALENE AND ITS DERIVATIVES. 467 

in the a-position ; it is prepared from a-naphthylamine or 
from naphthalene-a-sulphonic acid (p. 468). It is a colour- 
less, crystalline substance, melting at 94, and boiling at 280 ; 
it has a faint smell, recalling that of phenol, and it dissolves 
freely in alcohol and ether, but is only sparingly soluble in 
hot water. Its aqueous solution gives with ferric chloride a 
violet, flocculent precipitate, consisting probably of an iron 
compound of a-di-naphthol, OH-C 10 H 6 -C 10 H 6 -OH, an oxida- 
tion product of the naphthol. 

a-Naphthol, like phenol, is very readily acted on by nitric 
acid, yielding a ^'^'fro-derivative, C 10 H 5 (N0 2 ) 2 'OH, which 
crystallises in yellow needles, and melts at 138; this nitro- 
compound, like picric acid, has a much more strongly marked 
acid character than the hydroxy-compound from which it 
is derived, and decomposes carbonates, forming deep-yellow 
salts which dye silk a beautiful golden yellow ; its sodium 
derivative, C 10 H 5 (N0 2 ) 2 -ONa + H 2 0, is known commercially 
as Martius' yellow, or naphthalene yellow. Another dye 
obtained from a-naphthol is naphthol yelloiv (p. 538), 
the potassium salt of dinitro-a-naphtholsulphonic acid, 
C 10 H 4 (N0 2 ) 2 (OK).S0 3 K; the acid itself is manufactured 
by nitrating a-naphtholtrisulphonic acid (prepared by heat- 
ing a-naphthol with anhydrosulphuric acid), in which 
process two of the sulphoriic groups are displaced by nitro- 
groups. 

/3-Naphthol, prepared by fusing naphthalene-/2-sulphonic 
acid with potash, melts at 122, and boils at 286; it is a 
colourless, crystalline compound, readily soluble in hot water, 
and, like the a-derivative, it has a faint phenol-like smell. 
Its aqueous solution gives, with ferric chloride, a green 
colouration and a flocculent precipitate of /3-di-naphthol, 
OH.C 10 H 6 .C 10 H 6 -OH. 

Sulphonic Acids. Perhaps the most important derivatives 
of naphthalene, from a commercial point of view, are the 
various mono- and di-sulphonic acids, which are obtained 
from the hydrocarbon itself, from the naphthylamines, and 



468 NAPHTHALENE AND ITS DERIVATIVES. 

from the naphthols, and used in large quantities in the 
manufacture of dyes. It would be of little use to describe 
here the very numerous compounds of this class, but some 
indication of their properties may be afforded by a brief 
statement of the more important points. 

Naphthalene is readily sulphonated, yielding two mono- 
sulphonic acids, C 10 H 7 -S0 3 H, namely, the a- and ^-com- 
pounds, both of which are formed when the hydrocarbon 
is heated with concentrated sulphuric acid at 80; if, 
however, the operation be carried out at 160, only the 
/?-acid is obtained, because at this temperature the a-acid 
is converted into the /2-acid by intramolecular change, just 
as phenol-o-sulphonic acid is transformed into the ^9-acid 
by heating. The two naphthalenesulphonic acids are 
crystalline hygroscopic substances, and show all the charac- 
teristic properties of acids of this class. 

Di-sulphonic acids may be obtained by strongly heating 
naphthalene with sulphuric or anhydrosulphuric acid. 

Fourteen isomeric naphthylaminemonosulpJwnic acids, 
C 10 H 6 (NH 2 ).S0 3 H, may theoretically be obtained namely, 
seven from a-naphthylamine, and seven from the /3-base ; 
as a matter of fact, nearly all these acids are known. 
One of the most important, perhaps, is l:4-naphthylamine- 
monosulphonic acid, or naphthionic acid, which is the sole 
product of the action of sulphuric acid on a-naphthylamine ; 
it is a crystalline compound, very sparingly soluble in cold 
water, and is used in the manufacture of Congo-red (p. 537) 
and other dyes. 

The napJitholmonosidphonic acids correspond in number 
with the naphthylaminemonosulphonic acids, and are also 
extensively used in the colour industry. 

a-Naphthaquinone, C 10 H 6 2 , is a derivative of naphthalene 
corresponding with (benzo)quinone, and, like the latter, it 
is formed on oxidising various mono- and di-substitution 
products of the hydrocarbon with sodium dichromate and 
sulphuric acid, but only those in which the substituting 



NAPHTHALENE AND ITS DERIVATIVES. 469 

groups occupy the a-positions ; a-naphthylamine, 1 : 4-amido- 
naphthol, and l:4-diamidonaphthalene, for example, may 
be employed. As a rule, however, naphthalene itself is 
oxidised with a boiling solution of chromic acid in acetic 
acid (a method not applicable for the preparation of quinone 
from benzene), as the product is then easily obtained in a 
state of purity. 

a-Naphthaquinone crystallises from alcohol in deep-yellow 
needles, melting at 125; it resembles qninone in colour, 
in having a curious pungent smell, and in being very 
volatile, subliming readily even at 100, and distilling rapidly 
in steam. Unlike quinone, it is not reduced by sulphurous 
acid, but some reducing agents convert it into 1 : 4-dihydroxy- 
naphthalene, C 10 H 6 (OH) 2 , just as quinone is transformed 
into hydroquinone (p. 426). This close similarity in proper- 
ties clearly points to a similarity in constitution, so that 
a-naphthaquinone may be represented by the formula, 




/5-Naphthaquinone, C 10 H 6 2 , isomeric with the a-com- 
pound, is formed when a-amido-/?-naphthol is oxidised with 
potassium dichromate and dilute sulphuric acid, or with 
ferric chloride ; it crystallises in red needles, decomposes 
at about 115 without melting, and on reduction with sul- 
phurous acid, is converted into 1 : 2-dihydroxynaphthalene. 
It differs from a-naphthaquinone and from quinone in colour, 
in having no smell, and in being non-volatile, properties 
which, though apparently insignificant, are really of some 
importance, as showing the difference between or/fto-quinones 
and jpara-quinones ; the latter are generally deep-yellow, 
volatile compounds, having a pungent odour, whereas the 
former are red, non-volatile, and odourless. /^-Naphtha- 



470 NAPHTHALENE AND ITS DERIVATIVES. 

quinone is an example of an orthoquinone, and its consti- 
tution may be represented by the formula, 




Both a- and /?-naphthaquinone are oxidised by nitric acid, 
giving 0-phthalic acid, a proof that in both compounds the 
two oxygen atoms are united with only one nucleus ; that the 
one is a para-, the other an or/fto-quinone is also established, 
but, for reasons similar to those stated more fully in the. 
case of quinone, the exact disposition of the various carbon 
affinities is unknown. 

The above description of some of the more important 
naphthalene derivatives will be sufficient to show the close 
relationship which these compounds bear to the correspond- 
ing derivatives of benzene ; although the former exist in a 
larger number of isomeric forms, they are, as a rule, pre- 
pared by the same methods as their analogues of the benzene 
series, and resemble them closely in chemical properties. 
It may, in fact, be stated that, as a rule, all general re- 
actions and generic properties of benzene derivatives are met 
with again in studying naphthalene derivatives. 



CHAPTEK XXXII. 

ANTHRACENE AND PHENANTHRENE. 

Anthracene, C 14 H 10 , is a hydrocarbon of great commercial 
importance, as it is the starting-point in the manufacture of 
alizarin, the colouring matter employed in producing Turkey- 
red dye ; it is prepared exclusively from coal-tar. The 
crude mixture of hydrocarbons and other substances known 



ANTHRACENE AND PHENANTHRENE. 471 

as '50 per cent, anthracene' (p. 308) is first distilled with 
one-third of its weight of potash from an iron retort; the 
distillate, which consists almost entirely of anthracene and 
phenanthrene, is then digested with carbon disulphide, when 
the phenanthrene dissolves, leaving the anthracene, which 
is further purified by crystallisation from benzene. 

Crude anthracene contains considerable quantities of cavbazole, 

C 6 H 4 \ 

I /NH, a colourless, crystalline substance, melting at 238, 

C 6 H 4 / 

and boiling at 355. On treatment with potash this substance is 



converted into a potassium derivative, I /NK, which remains 

C 6 H 4 / 

in the retort, or is decomposed on heating ; many other impurities, 
which cannot readily be separated by crystallisation, are also got 
rid of in this way. 

Anthracene crystallises from benzene in colourless, lustrous 
plates, which show a beautiful blue fluorescence ; it melts 
at 213, boils at 351, and dissolves freely in boiling 
benzene, but is only sparingly soluble in alcohol and ether. 
On mixing saturated alcoholic solutions of anthracene and 
picric acid, anthracene picrate, C 14 H 10 ,C 6 H 2 (N0 2 ) 3 -OH, is 
deposited in ruby -red needles, which melt at 138; this 
compound is resolved into its components when treated with 
a large quantity of alcohol (distinction from phenanthrene 
picrate, p. 481). 

Constitution. The behaviour of anthracene towards chlorine 
and bromine is, on the whole, similar to that of benzene and 
naphthalene that is to say, it yields additive or substitution 
products according to the conditions employed ; towards con- 
centrated sulphuric acid, also, it behaves like other aromatic 
compounds, and is converted into sulphonic acids. When 
treated with nitric acid, however, instead of yielding a 
nitro-derivative, as was to be expected from the molecular 
formula of the hydrocarbon (which, from the relatively 
small proportion of hydrogen, clearly indicates the presence 
of one or more closed-chains), it is oxidised to anthra- 



472 ANTHRACENE AND PHENANTHREXE. 

quinone, C 14 H 8 2 , two atoms of hydrogen being displaced by 
two atoms of oxygen; this change always takes place, even 
when dilute nitric acid, or some other oxidising agent, is 
employed, and as it is closely analogous to that which 
occurs in the conversion of naphthalene, C 10 H 8 , into a- 
naphthaquinone, C 10 H 6 2 (p. 468), it is an indication of 
the presence of a closed-chain, oxidation processes of this 
kind (namely, the substitution of oxygen atoms for an equal 
number of hydrogen atoms) being unknown in the case 
of fatty (open-chain) hydrocarbons. Another highly im- 
portant fact, owing to its bearing on the constitution of 
anthracene, is this, that, although the hydrocarbon and 
most of its derivatives are resolved into simpler substances 
only with very great difficulty, when this does occur one 
of the products is always some benzene derivative, usually 
phthalic acid. 

Now, if the molecule of anthracene contained only one 
benzene nucleus, or even if, like naphthalene, it contained 
two condensed nuclei, there would still be certain carbon 
and hydrogen atoms to be accounted for, and this could 
only be done by assuming the presence of unsaturated side- 
chains ; as, however, all experience has shown that such 
side-chains in benzene and in naphthalene are oxidised to 
carboxyl (compare p. 452) with the utmost facility, it is 
impossible to assume their presence in anthracene, a com- 
pound which is always oxidised to the neutral substance 
anthraquinone, without loss of carbon. Arguments of this 
kind lead, therefore, to the conclusion that the molecule 
of anthracene is composed only of combined or condensed 
nuclei ; as, moreover, the hydrocarbon may be indirectly 
converted into phthalic acid, it must be assumed that two 
of these nuclei are condensed together in the o-position, 
as in naphthalene. 

If, now, an attempt be made to deduce a constitutional 
formula for anthracene on this basis, and it be further 
assumed that all the closed-chains are composed of six 



ANTHRACENE AND PHENANTHRENE. 



473 



carbon atoms, as in naphthalene, the following formulae 
suggest themselves as the most probable, 

CH OH 





CH 



although, of course, neither could be accepted as final without 
further evidence. 

Experience has shown, however, that formula i. must be 
taken as representing the constitution of anthracene (for- 
mula ii. expressing that of phenanthrene, p. 481), because it 
accounts satisfactorily for all known facts amongst others, 
for a number of important syntheses of the hydrocarbon 
(see below), for the relation of anthracene to anthraquinone, 
and for the isornerism of the anthracene derivatives. It 
is, nevertheless, just as difficult to determine and to express 
the actual disposition of the fourth affinity of each carbon 
atom in anthracene as in the cases of benzene and naphtha- 
lene ; as, however, there are reasons for supposing that the 
state of combination of the two central CH groups (that 
is, those which form part of the central nucleus only) is 
different from that of all the others (inasmuch as they 
are generally attacked first), and that the two carbon atoms 
of these groups are directly -united, the above formula (i.) 
is usually written, 



or C 6 H 4 



the disposition of the fourth affinities of the carbon atoms 




474 ANTHRACENE AND PHENANTHRENE. 

in the two C 6 H 4 < groups being taken to be the same as 
in the centric formula for benzene.* 

Anthracene may be obtained synthetically in various ways. 
It is produced when benzyl chloride is heated with aluminium 
chloride, 



3C 6 H 6 .CH 2 C1 = C 6 Hc 6 H 4 + C 6 H 5 .CH 3 + 3HC1, 
X UJ / 

the hydranthracene (p. 475), which is formed as an inter- 
mediate product, 



C1C * = C A< C H 4 + 2HC1 ' 



being converted into anthracene by loss of hydrogen, which 
reduces part of the benzyl chloride to toluene, as shown in 
the first equation. Anthracene is also formed, together with 
hydranthracene and phenanthrene (p. 481), when ortho-hromo- 
benzyl bromide (prepared by brominating boiliny o-bromo- 
toluene, C 6 H 4 Br-CH 3 ) is treated with sodium, 



here, again, hydranthracene is the primary product, and from 
it anthracene is formed by loss of hydrogen. 

Another interesting synthesis may be mentioned namely, 
the formation of anthracene on treating a mixture of tetra- 
bromethane and benzene with aluminium chloride, 
BrCHBr 



All these methods of formation are accounted for in a simple 
manner with the aid of the above constitutional formula, the 
last one especially indicating that the two central carbon 

/ CH \ 
atoms are directly united ; the formula C 6 H 4 <^ I / /C 6 H 4 

will, therefore, be employed in describing the anthracene 
derivatives. 

* The letters or numbers serve to denote the constitution of the anthra- 
cene derivatives (p. 475). " 



ANTHRACENE AND PHENANTHRENE. 475 

Isomerism of Anthracene Derivatives. Further evidence 
in support of the above constitutional formula is afforded 
by the study of the isomerism of the substitution products 
of anthracene, although, in most cases, all the isomerides 
theoretically possible have not yet been prepared. 

When one atom of hydrogen is displaced, three isomerides 
may be obtained, since there are three hydrogen atoms (a,/3,y), 
all of which are differently situated relatively to the rest of 
the molecule; these mono-substitution products are usually 
distinguished by the letters a, /?, y, according to the position 
of the substituent (compare formula p. 473). When two 
atoms of hydrogen are displaced by similar atoms or groups, 
fifteen isomeric di-substitution products may be obtained. 

OTT 

Hydranthracene, C 6 H 4 <^pTT 2 ^>C 6 H 4 , a substance of little im- 

portance, is formed on reducing anthracene with boiling concen- 
trated hydriodic acid, or with sodium amalgam and water. It is a 
colourless, crystalline compound, melting at 106-108, and when 
heated with sulphuric acid it is converted into anthracene, the 
acid being reduced to sulphur dioxide. 

r^irf^i 

Anthracene dichloride, C 6 H 4 <jj,>C 6 H 4 ,like hydranthracene, 

is an additive product of the hydrocarbon ; it is obtained when 
chlorine is passed into a cold solution of anthracene in carbon 
disulphide, whereas at 100 substitution takes place, monockloran- 
thracene and dickloranthracene, 

/CC1\ /CC1 

and c 



being formed ; these substitution products crystallise in yellow 
needles, melting at 103 and 209 respectively, and they are both 
converted into anthraquinone on oxidation, a fact which shows 
the positions of the chlorine atoms. 

CO 
Anthraquinone, C 6 H 4 <_>C 6 H 4 , is formed, as already 

mentioned, on oxidising anthracene with chromic or nitric 
acid. It is conveniently prepared by dissolving anthracene 
(1 part) in boiling glacial acetic acid, and gradually adding a 
concentrated solution of chromic acid (2 parts) in glacial 



476 ANTHRACENE AND PHENANTHRENE. 

acetic acid. As soon as oxidation is complete the product is 
allowed to cool, and the anthraquinone, which separates in 
long needles, is collected and purified either by sublimation 
or by recrystallisation from acetic acid. 

Anthraquinone is manufactured by oxidising finely-divided 50 
per cent, anthracene,' suspended in water, with sodium dichromate 
and sulphuric acid. The crude anthraquinone is collected on a 
filter, washed, dried, and heated at 100 with 2-3 parts of concen- 
trated sulphuric acid, by which means the impurities are converted 
into soluble sulphonic acids, whereas the anthraquinone is not 
acted on. The almost black product is now allowed to stand in 
a damp place, when the anthraquinone gradually separates in 
crystals as the sulphuric acid becomes dilute ; water is then added, 
and the anthraquinone collected, washed, dried, and sublimed. 

Anthraquinone may be produced synthetically by treating 
a solution of phthalic anhydride (p. 439) in benzene, with a 
strong dehydrating agent, such as aluminium chloride, the 
reaction taking place in two stages ; o-benzoylbenzoic acid is 
first produced, 

H 6 = C 6 H 4 



o-Benzoylbenzoic Acid. 

but by the further action of the aluminium chloride (or when 
treated with sulphuric acid), this substance is converted into 
anthraquinone with loss of 1 molecule of water, 

C C H 4<QQQfl^ C 6 H 5 = VoH-^gQ^CoH-t + H 2 0. 
A B A B 

Anthraquinone contains, therefore, two C 6 H 4 <C groups, united 
by two CO<C groups. 

That the two CO<^ groups occupy the o-position in the one 
benzene ring (A) is known, because they do so in phthalic acid ; 
that they occupy the o-position in the second benzene ring (B) has 
been proved, as follows : When bromophthalic anhydride is treated 
with benzene and aluminium chloride, hromobenzoylbenzoic acid 
is produced, and this, when treated with sulphuric acid, yields 
bromanthraquinone, 



ANTHRACENE AND PHENANTHRENE. 477 

The formation of this substance from bromophthalic acid proves, 
as before, that the two C0<^ groups are united to the ring A in 
the o-position. 
Now, when bromanthraquinone is heated with potash at 160, 

CO 
it is converted into hydroxyanthraquinone, 



A B 

f^OOTT 
and this, with nitric acid, yields phthalic acid, ~, . TT>C 6 H 4 , the 

group A being oxidised ; therefore the two CO<^ groups are at- 
tached to B, as well as to A, in the o-position, and anthraquinone 
has the constitution represented above, a conclusion which affords 
strong support to the above views regarding the constitution of 
anthracene. 

Anthraquinone crystallises from glacial acetic acid in pale- 
yellow needles, melts at 285, and sublimes at higher tempera- 
tures; it is exceedingly stable, and is only with difficulty 
attacked by oxidising agents, by sulphuric acid, or by nitric 
acid. In all those properties which are connected with the 
presence of the two carbonyl-groups, anthraquinone resembles 
the aromatic ketones much more closely than it does the 
quinones. It has no smell, is by no means readily volatile, 
and is not reduced when treated with sulphurous acid ; unlike 
quinone, therefore, it is not an oxidising agent. 

When treated with more powerful reducing agents, however, it 
is converted into oxanthranol, C 6 H 4 <T^r,Q77T^>C 6 H 4 , one of the 

CO<^ groups becoming ^>CH-OH, just as in the reduction of 
ketones ; on further reduction the other CO<^ group undergoes a 

/^TT/QTT\ 

similar change, but the product, C 6 H 4 <\,C 6 H 4 , loses one 



molecule of water, yielding anthranol, C 6 H/ ^ ">C 6 H 4 , which 

^CH ' 

is finally reduced to hydranthracene ; when anthraquinone is dis- 
tilled with zinc-dust, anthracene is produced. 

Anthraquinone is only slowly acted on by ordinary sul- 
phuric acid even at 250, yielding anthraquinone-/8-mono- 

CO 
sulphonic acid, C 6 H 4 <^,,>C 6 H 3 -S0 3 H; but when heated 



478 ANTHRACENE AND PHENANTHRENE. 

with a large excess of anhydrosulphuric acid at 160-170, it 
yields a mixture of isomeric disulphonic acids, C 14 H 6 2 (S0 3 H) 2 . 

Sodium aiithraquinone-/3-monosu]phonate, which is used in such 
large quantities in the manufacture of alizarin (see below), is pre- 
pared by heating anthraquinone with an equal weight of anhydro- 
sulphuric acid (containing 50 per cent, of SO 3 ) in enamelled iron 
pots at 160. The product is diluted with water, filtered from 
unchanged anthraquinone, and neutralised with soda ; on cooling, 
sparingly soluble sodium anthraquinone-monosulphonate separates 
in glistening plates, and is collected in filter-presses. The more 
soluble sodium salts of the anthraquinone-disulphonic acids, which 
are always formed at the same time, remain in solution. 

Test for Anthraquinone. When a trace of finely-divided 
anthraquinone is mixed with dilute soda, a little zinc-dust 
added, and the mixture heated to boiling, an intense red 
colouration is produced, but on shaking in contact with air, 
the solution is decolourised; in this reaction oxanthranol 
(p. 477) is formed, and this substance dissolves in the alkali, 
forming a deep-red solution ; on shaking with air, however, it 
is oxidised to anthraquinone, which separates as a flocculent 
precipitate. 

r*o 

Alizarin, C 6 H 4 <^>C 6 H 2 (OH) 2 , or l:2-dihydroxy anthra- 
quinone, occurs in madder (the root of Rubia tinctorum), a 
substance which has been used from the earliest times for 
dyeing purposes, and which owes its tinctorial properties to 
two substances, alizarin and purpurin (see below), both of 
which are present in the root in the form of glucosides. 
Muberythric acid, the glucoside of alizarin, is decomposed 
when boiled with acids, or when the madder extract is 
allowed to undergo fermentation, with formation of alizarin 
and two molecules of glucose, 

C 26 H 28 14 + 2H 2 - C 14 H 8 4 + 2C 6 H 12 6 . 

Ruberythric Acid. Alizarin. 

A dye of such great importance as alizarin naturally attracted 
the attention of chemists, and many attempts were made to 
prepare it synthetically. This was first accomplished in 1868 



ANTHRACENE AND PHENANTHRENE. 479 

by Graebe and Liebermann, who found that alizarin could 
be produced by fusing l:2-dibromanthraquinone* with potash, 

PO PO 

C 6 H 4 < Jj >C 6 H 2 Br 2 + 2KOH - C 6 H 4 < ^ >C 6 H 2 (OH) 2 + 2KBr, 

but the process was not a commercial success. 

At the present day, however, madder is no longer used, 
and the whole of the alizarin of commerce is made from 
(coal-tar) anthracene in the following manner. 

Anthracene is first oxidised to anthraquinone, and the 
latter is converted into anthraquinone-^-sulphonic acid by the 
method already described (p. 477) ; the sodium salt of this acid 
is then heated with soda and a little potassium chlorate, and 
is thus converted into the sodium derivative of alizarin, 



+ 2H 2 23 

from this sodium salt alizarin is obtained by adding acid. 

When anthraquinonesulphonic acid is fused with soda, the 
-SO 3 H group is displaced by -ONa in the usual manner, but 
the hydroxyanthraquinonc (sodium derivative) thus produced is 
further acted on by the soda, giving alizarin (sodium derivative) 
and hydrogen, 

PO PO 

C 6 H 4 <o>C 6 H 3 (ONa) + NaOH = C 6 H 4 <^>C 6 H 2 (ONa) 2 + H. 

The oxidising agent (KC10 3 ) is added in order to prevent the 
nascent hydrogen reducing the still unchanged hydroxyanthra- 
quinone to anthraquinone, the operation being conducted as 
follows. 

Sodium anthraquinonesulphonate (100 parts) is heated in a 
closed iron cylinder, fitted with a stirrer, with soda (300 parts) 
and potassium chlorate (14 parts), for two days at 180. The dark- 
violet product, which contains the sodium salt of alizarin, is dis- 
solved in water, the solution filtered if necessary, and the alizarin 
precipitated by the addition of hydrochloric acid. The yellowish 
crystalline precipitate is collected in filter-presses, washed well with 

* Obtained by heating anthraquinone with bromine and a trace of iodine 
in a sealed tube at 160. 



480 ANTHRACENE AND PHENANTHRENE. 

water, and sent into the market in the form of a 10 or 20 per cent, 
paste. From this product alizarin is obtained in a pure state by 
recrystallisation from toluene, or by sublimation. 

Alizarin crystallises and sublimes in dark-red prisms, 
which melt at 290, and are almost insoluble in water, but 
moderately soluble in alcohol. It is a dihydroxy-derivative 
of anthraquinone, and has therefore the properties of a 
dihydric phenol; it dissolves in potash and soda, forming 

CO 
metallic derivatives of the type C 6 H 4 <Cp r .^ > C 6 H 2 (OM) 2 , which 

are soluble in water, yielding intensely purple solutions. 
With acetic anhydride it gives a diacetate, C 14 H 6 2 (C 2 H 3 2 ) 2 , 
melting at 180, and when distilled with zinc-dust it is 
reduced to anthracene. 

The value of alizarin as a dye lies in the fact that it yields 
coloured, insoluble compounds ('lakes,' p. 518) with certain 
metallic oxides ; the ferric compound, for example, is violet 
black, the lime compound blue, and the tin and aluminium 
compounds different shades of red (Turkey-red). A short 
account of the methods used in dyeing with alizarin is given 
later (p. 516). 

Constitution of Alizarin. Alizarin may be prepared by 
heating a mixture of phthalic anhydride and catechol with 
sulphuric acid at 150, 



CO' 

As catechol is o-dihydroxy benzene, it follows that the two 
hydroxyl-groups in alizarin must be in the o-position to one 
another, and this substance must, therefore, be represented by 
one of the following formulas, 

CO 

^>^ 

iOH 





ANTHRACENE AND PHENANTHRENE. 481 

Now, alizarin yields two isomeric ?7zowo-nitro-derivatives, 

ro 

C 6 H 4 <^>C 6 H(OH) 2 -N0 2 , both of which contain the nitro- 

group in the same nucleus as the two hydroxyl-groups ; its 
constitution must, therefore, be represented by formula i., as 
a substance having the constitution u. could only yield one 
such nitro-derivative. 

Besides alizarin, several other dihydroxy- and also trihydroxy- 
anthraquinones have been obtained, but only those are of value as 
dyes which contain two hydroxyl-groups in the same positions as in 
alizarin ; two such derivatives, which possess very valuable dyeing 
properties, may be mentioned. 

CO 
Purpurin, C 6 H 4 < CO >C 6 H(OH) 3 , or 1 :2:4-trihydroxyanthraquin- 

one, is contained in madder, in the form of a glucoside, and may 
be prepared by oxidising alizarin with manganese dioxide and 
sulphuric acid. It crystallises in deep-red needles, melts at 253, 
and gives, with aluminium mordants, a much yellower shade of 
red than alizarin, and is now used on the large scale for the 
production of brilliant reds. 

Anthrapurpurin, C 6 H 3 (OH)<^~. >C 6 H 2 <^TT , is isomeric with 



purpurin, and is manufactured by fusing anthraquinone-disulphonic 

r*o 
acid, C 6 H 3 (SO 3 H)<Q>C 6 H 3 .SO 3 H, with soda and potassium 

chlorate (see alizarin, p. 479). It crystallises in yellowish-red 
needles, melts at 330, and is very largely employed in dyeing 
yellow shades of Turkey-red. 

Phenanthrene, C 14 H 10 , an isomeride of anthracene, is a 
hydrocarbon of considerable theoretical interest, although it 
has no commercial value. It occurs in large quantities in 
1 50 per cent, anthracene/ from which it may be extracted as 
already described (p. 470). The resulting crude phenanthrene 
is converted into the picrate, which is first recrystallised from 
alcohol, to free it from anthracene picrate, and then decom- 
posed by ammonia, the hydrocarbon being finally purified by 
recrystallisation. 

Phenanthrene crystallises in glistening needles, melts at 99, 

Org. Chem. 2 E 



482 ANTHRACENE AND PHENANTHRENE. 

and distils at about 340 ; it is readily soluble in alcohol, 
ether, and benzene. When oxidised with chromic acid, it 
is first converted into phenanthraquinone, C 14 H 8 2 , isomeric 
with anthraquinone, and then into diplienic acid, C 14 H 10 O 4 . 
This acid is decomposed on distillation with lime, yielding 
carbon dioxide and diphenyl (p. 350) ; it is therefore diphenyl- 
dicarboxylic acid, COOH-C 6 H 4 -C 6 H 4 -COOH, and its formation 
from phenanthrene shows that the latter contains two benzene 
nuclei. 

Further evidence as to the constitution of phenanthrene 
is obtained by studying its methods of formation. It is 
formed, for example, on passing o-ditolyl (prepared by treat- 
ing o-bromotoluerie with sodium) or stilbene* through a 
red-hot tube ; since these two hydrocarbons give the same 
product, the reactions must be expressed as follows, 

C fi H 4 (-'Ho CgH, CH 

I = I II + 2H 2 

C 6 H 4 CH 3 C 6 H 4 ^^ 

o-Ditolyl. Phenanthrene. 



CgHg CH CgH 4 CH 

li = I II 

C 6 H 5 CH C 6 H 4 CH 

Stilbene. Phenanthrene. 



H 2 . 



Again, phenanthrene is formed, together with anthracene, 
by the action of sodium on o-bromobenzyl bromide (p. 474), 

Br C 6 H 4 CH 2 Br C 6 H 4 CH 

Br C 6 H 4 CH 2 Br + ' C 6 H 4 C H 

* Stilbene, or diphenylethylene, C 6 H 5 -CH:CH-C 6 H 5 , may be prepared by 
acting on benzal chloride (p. 362) with sodium, 

2C 6 H 5 -CHCl 2 +4Na=C 6 H 5 -CH:CH-C 6 H 5 +4NaCl. 

It crystallises in colourless needles, melts at 120, and, like ethylene, 
combines with two atoms of bromine, forming stilbcne dibromide, 

C 6 H 5 -CHBr-CHBr-C 6 H 5 (m.p. 237), 



ANTHRACENE AND PHENANTHRENE. 



483 



For these and many other reasons, the constitution of phenan- 
threne is expressed by the formula, 



CH = CH 




When the hydrocarbon is oxidised to phenanthraquinone, 
the group -CH = CH- becomes -CO CO-, and, on further 
oxidation to diphenic acid, each carbonyl-group is converted 
into a carboxyl-group, 



co -co 




C0 2 H C0 2 H 




Phenanthraquinone. 



Diphenic Acid. 



C,H 4 CO 

Phenanthraquinone, i I , like anthraquinone, is 

C 6 H 4 CO 

formed by oxidising the hydrocarbon with chromic acid. It 
crystallises from alcohol in orange needles, and melts at 198. 
In chemical properties it shows little resemblance to quinone 
or to a-naphthaquinone, but is closely related to /?-naphtha- 
quinone (p. 469), and is, like the latter, an ortho-diketone 
(ortho-quinone) ; it has no smell, and does not volatilise except 
when strongly heated, but it is readily reduced by sulphurous 
acid to dihydroxyphenanthrene, C 14 H 8 (OH) 2 , and it combines 
with sodium bisulphite, forming a soluble bisulphite com- 
pound, C 14 H 8 2 , NaHS0 3 + 2H 2 ; with hydroxylamine it 
yields a dioxime, C 12 H 8 (C:NOH) 2 . The hydroxy-derivatives 
of phenanthraquinone, unlike those of anthraquinone, possess 
no tinctorial properties. 

Phenanthraqninone may be readily detected by dissolving a 
small quantity (0-1 gram) in glacial acetic acid (20 c.c.), adding a 



484 ANTHRACENE AND PHENANTHRENE. 

few drops of commercial toluene, and then mixing the well-cooled 
solution with sulphuric acid (1 c.c. ). After standing for a few 
minutes, the bluish-green liquid is poured into water and shaken 
with ether, when the ether acquires an intense reddish-violet 
colouration (Laubenheimer's reaction). Like the indophenin reac- 
tion, this test depends on the formation of a colouring matter 
containing sulphur, produced hy the condensation of the phenan- 
thraquinone with the thiotolene, C 4 H 3 S(CH 3 ), which is contained in 
crude toluene (p. 344). 

C 6 H 4 COOH 

Diphenic acid, I , obtained by the oxidation 

C 6 H 4 COOH 

of phenanthrene or of phenanthraquinone with chromic acid, 
crystallises from water in needles, and melts at 229. When 
heated with acetic anhydride it is converted into dipJienic 

PO 

anhydride, C 12 H 8 <:|::>0 (m.p. 217). 
\j\j 

This fact is remarkable, because it shows that in the case of de- 
rivatives of hydrocarbons which are composed of condensed benzene 
nuclei, the ortho-position is not the only one which allows of 
the formation of an anhydride. Naphthalic acid, C 10 H 6 (COOH) 2 , 
a derivative of naphthalene in which the carboxyl-groups are in 
the 1 :!'- or peri-position, also forms an anhydride. 



CHAPTER XXXIII. 

PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 

Pyridine, quinoline, and isoquinoline are three very in- 
teresting aromatic bases, which, together with their numerous 
derivatives, form a group of great theoretical interest, and of 
scarcely less importance than that of the aromatic hydro- 
carbons ; many of these derivatives occur in nature, and 
belong to the well-known and important class of compounds 
known as 'alkaloids.' 

Coal-tar, though consisting principally of hydrocarbons and 



PYRIDINE, QUINOLINE, AND ISOQUINOL1NE. 485 

phenols, contains also small quantities of pyridine and its 
homologues, quinoline, isoquinoline, and numerous other basic 
substances, such as aniline ; all these bases are dissolved, in 
the form of sulphates, in the purification of the hydro- 
carbons, &c., by treatment with sulphuric acid (compare 
p. 307), and, if the dark^ acid liquor be afterwards treated 
with excess of soda, they separate again at the surface of the 
liquid in the form of a dark-brown oil. By repeated frac- 
tional distillation a partial separation of the various con- 
stituents of this oil may be effected, and crude pyridine, 
quinoline, &c., may be obtained; on further purification by 
crystallisation of their salts, or in other ways, some of these 
bases may be prepared in a state of purity. 

Another important source of these compounds is bone-tar 
or l)one-oil y a dark-brown, unpleasant-smelling liquid formed 
during the dry distillation of bones in the preparation of 
bone-black (animal charcoal) ; this oil contains considerable 
quantities of pyridine and quinoline, and their homologues, as 
well as other bases, and these compounds may be extracted 
from it with the aid of sulphuric acid, and then separated in 
the manner mentioned above. Bone-oil, purified by distilla- 
tion, was formerly used in medicine under the name of 
Dippel's oil. 

Pyridine and its Derivatives. 

Pyridine, C 5 H 5 N, is formed during the destructive distilla- 
tion of a great variety of nitrogenous organic substances ; 
hence its presence in coal-tar and in bone-oil. 

Pure pyridine is conveniently prepared in small quantities 
by distilling nicotinic acid (p. 492), or other pyridinecarboxylic 
acid, with lime, just as pure benzene may be prepared from 
benzoic and phthalic acids in a similar manner, 
C 6 H 4 N.COOH - C 5 H 5 N + C0 9 
C 5 H 3 N(COOH) 2 = C 5 H 5 N + 2C0 2 . 

For commercial purposes it is usually prepared by the repeated 
fractional distillation of the basic mixture, which is separated 



486 PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 

from bone-oil or coal-tar as already described ; the product 
consists of pyridine, together with small quantities of its 
homologues. 

Pyridine is a colourless, mobile liquid of sp. gr. 1-003 at 
0; it boils at 115, is miscible with water in all proportions, 
and possesses a pungent and very characteristic odour. It 
is an exceedingly stable substance, as it is not attacked by 
boiling nitric or chromic acid, and only with difficulty by halo- 
gens; in the latter case substitution products such as mono- 
bromopyridine, C 5 H 4 BrN, and dibromopyridine, C 5 H 3 Br 2 N, 
are formed. If, however, a solution of pyridine in hydro- 
chloric acid be treated with bromine, a crystalline, unstable 
additive product, C 5 H 5 NBr 2 , is precipitated, even from very 
dilute solutions, and the formation of this substance is 
sometimes used as a test for pyridine. 

When dissolved in alcohol and treated with sodium, 
pyridine is readily reduced, piperidine or hexaliydropyridine 
(p. 489) being formed, 



Pyridine is a strong base ; like the amines, it turns red 
litmus blue, and combines with acids to form crystalline salts, 
such as the hydrochloride, C 5 H 5 Isr,HCl, and the sulphate, 
(C 5 H 5 N) 2 ,H 2 S0 4 . The platinichloride, (C 5 H 5 N) 2 ,H 2 PtCl 6 , 
crystallises in orange-yellow needles, and is readily soluble 
in water ; when, however, its solution is boiled, a very 
sparingly soluble yellow salt, (C 5 H 5 N) 2 PtCl 4 , separates, a 
fact which may be made use of for the detection of pyridine 
even when only small quantities of the base are available. 
Another test for pyridine (and its homologues) consists in 
heating a, few drops of the base in a test tube with methyl 
iodide, when a vigorous reaction takes place, and a yellowish 
additive product, 'pyridine metliiodide, C 5 H 5 N,CH 3 I, is pro- 
duced ; if a piece of solid potash be now added, and the 
contents of the tube again heated, a most pungent and 
exceedingly disagreeable smell is at once noticed. 



PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 487 

Constitution. Pyridine is a strong base, has a pungent 
odour, and turns red litmus blue, properties which at once 
suggest some relation to the amines. It is not, however, a 
primary amine, because it does not give the carbylamine re- 
action ; nor is it a secondary amine, because it is not acted on 
by nitrous acid ; the necessary conclusion that pyridine is a 
tertiary base is further borne out by its behaviour towards 
methyl iodide. But since pyridine has the molecular formula, 
C 5 H 5 N, it is obvious that it cannot be an open-chain tertiary 
base, because no reasonable constitutional formula based on 
this view could be constructed. If, moreover, it be borne in 
mind that pyridine is extremely stable, the probability of its 
being a fatty (open-chain) compound at all seems very remote, 
because if it were it would be highly unsaturated, and should 
be readily oxidised and resolved into simpler substances. 
The grounds for doubting its relation to any fatty compound 
are, in fact, much the same as those which led to the con- 
clusion that the constitution of benzene is totally different 
from that of dipropargyl (p. 314). 

Comparing now the properties of pyridine with those of 
aromatic compounds, a general analogy is at once apparent ; 
in spite of its great stability, pyridine shows, under certain 
conditions, the behaviour of an unsaturated compound, and, 
like benzene, naphthalene, and other closed-chain compounds, 
yields additive products, such as piperidine. 

Considerations such as these led to the conclusion, suggested 
by Korner in 1869, that pyridine, like benzene, contains a 
closed-chain or nucleus, as represented by the following 
formula, 




and this view has since been confirmed in a great many ways, 
notably in the following manner: Piperidine, or hexahydro- 



488 PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 

pyridine, the compound which is formed by the reduction 
of pyridine, and which is reconverted into the latter on 
oxidation with sulphuric acid (p. 490), has been prepared 
synthetically by a method (p. 490) which shows it to have the 
constitution (i.) ; pyridine, therefore, has the constitution (11.), 
the relation between the two compounds being the same as 
that between benzene and hexahydrobenzene, 

CH 2 CH 

CH^ >H , 



CH 2 k JCH 2 CHL JOB 

NH N 

Piperidine (L). Pyridine (II.). 

That the constitution of pyridine is represented by this 
formula (u.) is also established by a study of the isomerism 
of pyridine derivatives, and by its relation to quinoline 
(p. 493); it must, therefore, be regarded as derived from 
benzene by the substitution of trivalent nitrogen N<; for one 
of the CH<; groups. 

The exact nature of the union of the nitrogen and carbon atoms 
is not known, and, as in the case of benzene, several methods of 
representation (some of which are shown below) have been sug- 
gested ; of these, the centric formula is perhaps the best, for 
reasons similar to those already mentioned in discussing the 
constitution of benzene (pp. 316-317). 



OH CH CH 




K^J ">I 



cn en CH 

N N N 

Korner. Dewar. Centric Formula. 

Isomerism of Pyridine Derivatives. The mowo-substitution 
products of pyridine, as, for example, the methylpyridines, 
exist in three isomeric forms ; this fact is clearly in accord- 
ance with the accepted constitutional formula for pyridine, in 
which, for the sake of reference, the carbon atoms may be 



PYBIDINE, QUINOLINE, AND ISOQUINOLINE. 489 

numbered or lettered * in the following manner, the symbols 
C and H being omitted as usual, 




These substitution products being formed by the displace- 
ment of any one of the five hydrogen atoms, it is evident 
that the following three, but not more than three, isomerides 
may be obtained, 






x 



The positions aa' are identical, and so also are the positions 
/?ft, but the position y is different from any of the others. 

The ^'-substitution products exist theoretically in six 
isomeric forms, the positions of the substituents in the 
several isomerides being as follows, 

aft ay, a/?', aa', ft3', fty. 

All other positions are identical with one of these ; aft for 
example, is the same as a'ft, and fly is identical with f$'y. 

As regards the isomerism of its derivatives, pyridine may 
be conveniently compared with a mono-substitution product 
of benzene aniline, for example the effect of substituting a 
nitrogen atom for one of the CH<: groups in benzene being 
the same, in this respect, as that of displacing one of the 
hydrogen atoms by some substituent. 

Derivatives of Pyridine. Piperidine, or hexahydropyridine, 
C 5 H 10 NH, is formed, as already stated, when pyridine is 
reduced with sodium and alcohol ; it is usually prepared 

* In the pyridine derivatives letters are generally used instead of 
numerals, the latter being conveniently reserved for benzene derivatives. 



490 PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 

from pepper, which contains the alkaloid pipenne (p. 503), a 
substance which is decomposed by boiling alkalies yielding 
piperidine and piperic acid. 

Powdered pepper is extracted with alcohol, the filtered solution 
evaporated, and the residue distilled with potash ; after neutralis- 
ing with hydrochloric acid, the distillate is evaporated to dryness, 
and the residue extracted with hot alcohol to separate the piperi- 
dine hydrochloride from the ammonium chloride which is always 
present. The filtered alcoholic solution is then evaporated, the 
residue distilled with solid potash, and the crude piperidine purified 
hy fractional distillation over potash. 

Piperidine is a colourless liquid, boiling at 106, and is 
miscible with water in all proportions, heat being developed ; 
it has a very penetrating odour, recalling that of pepper. 
Like pyridine, it is a very strong base, turns red litmus blue, 
and combines with acids forming crystalline salts ; when 
heated with concentrated sulphuric acid at 300 it loses six 
atoms of hydrogen, and is converted into pyridine, part of 
the sulphuric acid being reduced to sulphur dioxide. 

Piperidine behaves like a secondary amine towards nitrous 
acid, and yields nitroso-piperidine, C 5 H 10 N-NO, an oil, boiling 
at 218; like secondary amines, moreover, it interacts with 
methyl iodide, giving methylpiperidine, C 5 H 10 N-CH 3 ; it is, 
therefore, a secondary base (compare p. 496). 

The important synthesis of piperidine, which has already 
been referred to as establishing the constitution of the base, 
and also that of pyridine, was accomplished by Ladenburg 
in the following way. Trimethylene bromide* is heated 
with potassium cyanide in alcoholic solution, and thus con- 
verted into trimethylene cyanide, 



Br-CH 2 .CH 2 .CH 2 .Br + 2KCN = 



2KBr, 



* Trimethylene bromide, C 3 H 6 Br 2 , is prepared by treating allyl bromide 
(Part I. p. 262) with concentrated hydrobromic acid, 

CH 2 Br.CH:CH 2 +HBr=CH 2 Br-CH. 2 -CH 2 Br; 
it is a heavy, colourless oil, and boils at 164. 



PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 491 

a substance which, 011 reduction with sodium and alcohol, 
yields pcniametliylene diamine, just as methyl cyanide under 
similar conditions yields ethylamine, 



Ctf .CH .CH 2 -CH 2 .C]$r + 8H = 

im 2 .CH 2 .CH 2 -CH 2 .CH 2 .CH 2 .NH 2 ; 

during this reduction process some of the pentamethylene 
diamine is decomposed into piperidine and ammonia, and the 
same change occurs, but much more completely, when the 
hydrochloride of the diamine is distilled, 

r ^ ^CH 2 -CH 2 ^ 
'^CH^CH/ H 3" 

Homologues of Pyridine. The alkyl-derivatives of pyridine 
occur in coal-tar an'd bone-oil, and are therefore present in 
the crude pyridine obtained from the mixture of bases in 
the manner already referred to; they can only be isolated by 
repeated fractional distillation and subsequent crystallisation 
of their salts. The three (a, /3, y) isomeric methylpyridines 
or picolines, C 5 H 4 N-CH 3 , the six isomeric dimethylpyridines 
or lutidines, C 5 H 3 N(CH 8 ) 2 , and the trimethylpyridines or 
collidines, C 5 H 2 N(CH 3 ) 3 , resemble the parent base in most 
ordinary properties, but, unlike the latter, they undergo oxida- 
tion more or less readily on treatment with nitric acid or 
potassium permanganate, and are converted into pyridine- 
carboxylic acids, just as the homologues of benzene yield 
benzenecarboxylic acids, the alkyl-groups or side-chains being 
oxidised to carboxyl-groups, 

C 5 H 4 N-CH 3 + 30 = C 5 H 4 N-COOH + H 2 
C 5 H 3 N(CH 3 ) 2 + 60 = C 5 H 3 N(COOH) 2 + 2H 2 0. 
This behaviour is of great use in determining the positions of 
the alkyl-groups in these homologues of pyridine, because the 
carboxylic acids into which they are converted are easily 
isolated, and are readily identified by their melting-points 
and other properties. 

The pyridinecarboxyUc acids are perhaps, as a class, the 
most important derivatives of pyridine, chiefly because they 



-192 PYRIDINE, QUINOLINK, AND ISOQUINOLINE. 

are obtained as decomposition products on oxidising many of 
the alkaloids. 

The three (a, /?, y) monocarboxylic acids may be prepared 
by oxidising the corresponding picolines or methylpyridines 
(see above) with potassium permanganate. The a-carboxylic 
acid is usually known as picolinic acid, because it was first 
prepared from a-picoline (a-methylpyridine), whereas the 
^-compound is called nicotinic acid, because it was first 
obtained by the oxidation of nicotine (p. 502) ; the third 
isomeride namely, the y-carboxylic acid is called isonicotinic 

acid, and is the oxidation product of y-picoline. 

COOH 

COOH 






J COOH 

N N 

Picolinic Acid, or Nicotinic Acid, or Isonicotinic Acid, or 

Pyridine-a-carboxylic Acid Pyridine-/3-carboxylic Acid Pyridine-y-carboxylic Acid 
(111. p. 136). (in. p. 229). (sublimes without melting). 

These moriocarboxylic acids are all crystalline and soluble 
in water ; they have both basic and acid properties, and form 
salts with mineral acids as well as with bases, a behaviour 
which is similar to that of glycine (Part I. p. 299). 

The a-carboxylic acid, and all other pyridinecarboxylic 
acids which contain a carboxyl-group in the a-position (but 
only such), give a red or yellowish-red colouration with ferrous 
sulphate, a reaction which is of great value in determining 
the positions of the carboxyl-groups in such compounds. 

A carboxyl-group in the a-position, moreover, is usually 
very readily eliminated on heating; picolinic acid, for 
example, is much more readily converted into pyridine 
than nicotinic or isonicotinic acid. 

Quinolinic acid, C 5 H 3 N(COOH) 2 (pyridine-a/3-dicarboxylic 
acid), 

iCOOH 

COOH 




PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 493 

a compound produced by the oxidation of quinoline with 
potassium permanganate, is the most important of the six iso- 
meric dicarboxylie acids. It crystallises in colourless prisms, 
is only sparingly soluble in water, and gives, with ferrous sul- 
phate, an orange colouration, one of the carboxyl-groups being 
in the a-position. When heated at 190 it decomposes into 
carbon dioxide and nicotinic acid, a fact which shows that 
the second carboxyl-group is in the /3-position. On distilla- 
tion with lime, quinolinic acid, like all pyridinecarboxylic 
acids, is converted into pyridine. 

In its behaviour when heated alone, quinolinic acid differs 
in a marked manner from phthalic acid the corresponding 
benzenedicarboxylic acid as the latter is converted into 
its anhydride (p. 439) ; nevertheless, when heated with 
acetic anhydride, quinolinic acid gives an anhydride, 

CO 

, a colourless, crystalline substance, melting 



at 134. This fact shows that the carboxyl-groups are united 
with carbon atoms, which are themselves directly united (as 
in the case of phthalic acid), and is further evidence in 
support of the constitutional formula given above. 

Quinoline. 

Quinoline, C 9 H 7 ]Sr, occurs, together with isoquinoline, in 
that fraction of coal-tar and bone-oil bases (p. 485) which is 
collected between 236 and 243 ; as, however, it is difficult 
to obtain the pure substance from this mixture, quinoline 
is usually prepared synthetically, by a method devised 
by Skraup namely, by heating a mixture of aniline and 
glycerol with sulphuric acid and nitrobenzene. 

Concentrated sulphuric acid (100 parts) is gradually added to a 
mixture of aniline (38 parts), nitrobenzene (24 parts), and glycerol 
(120 parts), and the mixture is then very cautiously heated in a 
large flask (with reflux apparatus) on a sand-bath ; after the very 
violent reaction which soon sets in has subsided, the liquid is kept 
boiling for about four hours. It is then cooled, diluted with water, 



494 PYRIDINE, QU1NOLINE, AND ISOQUINOL1NE. 

and the unchanged nitrobenzene separated by distillation in steam ; 
soda is then added in excess to liberate the quinoline and the 
unchanged aniline from their sulphates, and the mixture is again 
steam-distilled. As these two bases cannot well be separated by 
fractional distillation, the whole of the aqueous distillate is acidi- 
fied with sulphuric acid, and sodium nitrite added until nitrous 
acid is present after shaking well (p. 385) ; after heating, to convert 
the diazo-salt into phenol, the solution is rendered alkaline with 
soda and again submitted to distillation in steam. The quinoline 
in the receiver is finally separated with the aid of a funnel, dried 
over solid potash, and purified by fractional distillation. 

Qninoline is a colourless, highly refractive oil, of sp. 
gr. 1-095 at 20, and boils at 239. It has a peculiar 
characteristic smell, and is sparingly soluble in water, 
but it dissolves freely in dilute acids, forming crystalline 
salts, such as the hydrochloride, CgH^NjHCl, the sulphate, 
(C 9 H 7 N) 2 ,H 2 S0 4 , &c. It also forms double salts, of which 
the platinichloride, (C 9 H 7 N) 2 ,H 2 PtCl 6 + 2H 2 0, and the di- 
chromate, (CgH^N^HgCrgOf, may be mentioned ; the latter, 
prepared by adding potassium dichromate to a solution of 
quinoline hydrochloride, crystallises from water, in which 
it is only sparingly soluble, in glistening yellow needles, 
melting at 165. 

Constitution. Quinoline is alkaline to litmus, but it does 
not give the reactions of a primary nor those of a secondary 
base ; on the other hand, it combines with methyl iodide to 
form the additive product, quinoline methiodide, C 9 H 7 N,CH 3 I, 
and in this and other respects shows the behaviour of a 
tertiary base. Now, as the relation between pyridine, C 5 H 5 N, 
and quinoline, C 9 H r N, on the one hand, is much the same as 
that between benzene, C 6 H 6 , and naphthalene, C 10 H 8 , on the 
other, both as regards molecular composition (the difference 
being C 4 H 2 in both cases) and chemical behaviour, and as, 
consequently, quinoline cannot be an open-chain compound, 
it might be assumed that quinoline is derived from pyridine, 
just as naphthalene is derived from benzene ; its constitution 
would then be expressed by one of the following formulae, 



PYRIDINE, QU1NOLINE, AND ISOQUINOLTNE. 



495 



CH 



CH 



01 1 




CH 




on 



Now, quinoline differs from pyridine, just as naphthalene 
differs from benzene, in being much more readily oxidised, 
and when heated with an alkaline solution of potassium perman- 
ganate it yields quinolinic acid, C 5 H 3 N(COOH) 2 , a derivative 
of pyridine (p. 492) ; this fact proves that quinoline contains 
a pyridine nucleus ; but it also contains a benzene nucleus, as 
is shown by its formation from aniline by Skraup's method. 
Its constitution, therefore, must be expressed by one of the 
above formulae, as these facts admit of no other interpretation. 
As, moreover, the carboxyl-groups in quinolinic acid are in the 
apposition (compare p. 493), formula n. is inadmissible, a 
conclusion which is obviously necessary to explain the forma- 
tion of quinoline from aniline. For these and other reasons, 
the constitution of quinoline is represented by formula I. (the 
other expressing that of isoquinoline). 

The formation of quinoline from aniline and glycerol may be 
explained as follows : The glycerol and sulphuric acid first 
interact, yielding acrolein (Part I. p. 262), which then con- 
denses with aniline (as do all aldehydes), forming acrylaniline, 
C 6 H 5 .NH 2 + CHO.CH:CH 2 - C 6 H 5 .N:CH.CH:CH 2 + H 2 ; 
this substance, under the oxidising action of the nitro- 
benzene,* loses two atoms of hydrogen, and is converted into 
quinoline, 

CH CH 

-jun 

+ H 2 0. 



CH 




* Nitrobenzene is often employed as a mild oxidising agent, as in 
presence of an oxidisable substance it is reduced to aniline, 
CgH -NO 8 + 6H = C 6 H 5 -N H 2 + 2H 2 O. 



496 PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 

Many derivatives of quinoline may be obtained by Skraup's 
reaction, using derivatives of aniline instead of the base 
itself ; when, for example, one of the three toluidines (p. 376) 
is employed, a methylquinoline is formed, the position of the 
methyl-group which is, of course, united with the benzene, 
and not with the pyridine nucleus depending on which of 
the toluidines is taken. 

Isoquinoline, C 9 H 7 N, occurs in coal-tar quinoline, and may 
be isolated by converting the fraction of the mixed bases, 
boiling at 236-243, into the acid sulphates, C 9 H 7 N,H 2 S0 4 , 
and recrystallising these salts from alcohol (88 per cent.) 
until the crystals melt at 205. The sulphate of isoquinoline 
thus obtained is decomposed by potash, and the base puri- 
fied by distillation. Isoquinoline is very like quinoline in 
chemical properties^ but it is solid, and melts at 23 ; its 
boiling-point, 241, is also slightly higher than that of 
quinoline (239). 

The constitution of isoquinoline is very clearly proved by 
its behaviour on oxidation with permanganate, when it yields 
both phthalic acid and cinchomeronic acid, C 5 H 3 N(COOH) 2 , 
or pyridine-^y-dicarboxylic acid ; oxidation takes place, there- 
fore, in two directions, in the one case the pyridine (Py), in 
the other the benzene (B), nucleus being broken up, 

CH CH CH CH 

^ 





c-COOH COOH-c 
CH CH CH CH 

Isoquinoline. Phthalic Acid. Cinchomeronic Acid. 

Aromatic Bases. It will be seen from the above description of 
piperidme, pyridine, and quinoline that aromatic bases which owe 
their basic character to the group ^>NH or ^N forming part of a 
closed-chain show the same chemical behaviour as open-chain, 
secondary, or tertiary bases respectively, as far as these particular 
groups are concerned. 

The secondary bases, such as piperidine, which contain the 



PYRIDINE, QUINOLINE, AND ISOQUINOLINE. 497 

>NH-group, yield nitroso-derivatives, and when warmed with 
an alkyl halogen compound they are converted into alkyl- 
derivatives by the substitution of an alkyl-group for the hydrogen 
atom of the ^>NH -group, 

>NH + CH 3 I=>N.CH 3 ,HI, 

just as diethylamine, for example, interacts with ethyl iodide, 
giving triethylamine, 

(C 2 H 5 ) 2 NH + C 2 H 5 I = (C 2 H 5 ) 2 N.C 2 H 5 ,HI. 

These alkyl-derivatives of the secondary bases are themselves 
tertiary bases, and have the property of forming additive products 
with alkyl halogen compounds, giving salts corresponding with the 
quaternary ammonium salts (Part I. pp. 209, 210), 

>N.CH 3 + CH 3 I=>N.CH 3 ,CH 3 I, or >N(CH 3 ) 2 I. 
The hydrogen atom of the >NH-group in secondary bases of this 
kind is also displaceable by the acetyl-group and by other acid 
radicles. 

The tertiary bases, such as pyridine and quinoline, in which the 
nitrogen atom is not directly united with hydrogen, do not yield 
nitroso- or acetyl-derivatives, but they unite with one molecule of 
an alkyl halogen compound giving additive compounds, correspond- 
ing with the quaternary ammonium salts. 



CHAPTER XXXIV. 

ALKALOIDS. 

The term alkaloid is generally applied to those basic nitro- 
genous substances which occur in plants, irrespective of any 
similarity in properties or constitution ; as, however, most 
substances of this kind have some important physiological 
action, the use of the word may be restricted in this sense. 

Most alkaloids are composed of carbon, hydrogen, oxygen, 
and nitrogen, have a high molecular weight, and are crystalline 
and non-volatile, but a few, notably coniine and nicotine, are 
composed of carbon, hydrogen, and nitrogen only, and are 
volatile liquids ; with the exception of these liquid com- 
pounds, which are readily soluble, the alkaloids are usually 

Org. Chem. '2 F 



498 ALKALOIDS. 

sparingly soluble in water, but dissolve much more readily in 
alcohol, chloroform, ether, and other organic solvents ; they 
are all soluble in acids, with which they usually form well- 
defined, crystalline salts. Many alkaloids have a very bitter 
taste, and are excessively poisonous ; many, moreover, are 
extensively used in medicine, and their value in this respect 
can hardly be overrated. 

Generally speaking, the alkaloids are tertiary aromatic bases, 
but the constitutions of many of them have not yet been 
established in detail, owing partly to their complexity, partly 
to the difficulties which are experienced in resolving them 
into simpler compounds which throw any light on the 
structure of their molecules. It is known, however, that 
many alkaloids are derivatives of pyridine, quinoline, or 
isoquinoline. 

It is a remarkable fact that by far the greater number 
of alkaloids contain one or two, sometimes three or more, 
methoxy -groups (-0-CH 3 ), united with a benzene nucleus 
(as in anisole, C 6 H 5 -0-CH 3 , p. 405), and the determination 
of the number of such groups in the molecule is of the 
greatest importance as a step in establishing the constitution 
of an alkaloid, because in this way some of the carbon, 
oxygen, and hydrogen atoms are at once disposed of. The 
method employed for this purpose depends on the fact that 
all substances containing methoxy-groups are decomposed 
by hydriodic acid, yielding methyl iodide and a hydroxy- 
compound (compare anisole) in accordance with the general 
equation, 

<-OCH 3 ) + nKI = rc(-OH) + rcCH 3 I ; 

by estimating the methyl iodide obtained from a given 
quantity of a compound of known molecular weight, it is 
easy, therefore, to determine the number of methoxy-groups 
in the molecule ; ethoxy-groups may also be determined in a 
similar manner. 

This method was first applied by Zeisel, and is of general 
application, as it affords a means of accurately determining 



ALKALOIDS. 499 

the number of methoxy-groups, not only in alkaloids, but 
in any other substances in which they occur; it is carried 
out as follows : 

A distilling flask of about 35 c.c. capacity (, fig. 24), with the 
side-tube bent as shown, and suspended in a beaker of glycerol, 
is fixed to the condenser (6) by means of a cork, and connected 
with an apparatus for generating carbon dioxide. 

The condenser, through which water at 50 circulates from the 
bottle (c), is attached to the 'potash bulbs,' which contain water 
and about 0-5 gram of amorphous phosphorus ; the bulbs are 
suspended in a beaker of water kept at 60, and connected, as 
shown, with two flasks (d, e), containing respectively 50 c.c. and 
25 c.c. of an alcoholic solution of silver nitrate (prepared by adding 
100 c.c. of absolute alcohol to a solution of 5 grams of silver nitrate 
in 12 c.c. of water). 

About 0-3 gram of the substance under examination is placed in 
the flask (a), together with 10 c.c. of distilled hydriodic acid (free 
from sulphur compounds), and the temperature of the glycerol bath 
is gradually raised, until the acid just boils, carbon dioxide, at the 
rate of about 3 bubbles in 2 seconds, being passed all the time. 

The methyl iodide is carried forward through the 'potash bulbs,' 
where it is freed from hydriodic acid and small quantities of iodine, 
and then into the alcoholic silver nitrate, where it is decomposed 
with separation of silver iodide. The operation, which occupies 
about two hours, is at an end when the precipitate in the flask 
settles, and leaves a clear, supernatant liquid. 

The contents of flask e are poured into 5 vols. of water and 
gently warmed; if, as is usually the case, no precipitation take 
place after five minutes, the solution is neglected ; if, however, a 
precipitate form, it must be collected and added to that contained 
in flask d. The alcoholic liquid in flask d is decanted from the 
precipitate, mixed with water (300 c.c.) and a few drops of nitric 
acid, and heated to boiling until free from alcohol ; any precipi- 
tate is then added to the main quantity, the whole digested for a 
few minutes with dilute nitric acid, collected, dried, and weighed. 

Example. 0-3726 gram of substance gave 0-8164 gram of silver 
iodide, which corresponds with 28-9 per cent, of -OCH 3 ; the sub- 
stance was C 8 H 4 O 3 (OCH 3 ) 2 . 

The extraction of alkaloids from plants, and their subse- 
quent purification, are frequently matters of considerable 
difficulty, partly because in many cases a number of alkaloids 



ALKALOIDS. 501 

occur together, partly because of the neutral and acid sub- 
stances, such as the glucosides, sugars, tannic acid, malic acid, 
&c., which are often present in large quantities. Generally 
speaking, they may be extracted by treating the macerated 
plant or vegetable product with dilute acids, which .dissolve 
out the alkaloids in the form of salts ; the filtered solution 
may then be treated with soda to liberate the alkaloids, 
which, being sparingly soluble, are usually precipitated, and 
may be separated by filtration ; if not, the alkaline solution 
is extracted with ether, chloroform, &c. The products are 
finally purified by recrystallisation, or in some other manner. 

Most alkaloids give insoluble precipitates with a solution 
of tannic, picric, phosphomolybdic, or phosphotungstic acid, 
and with a solution of mercuric iodide in potassium iodide, * 
&c. ; these reagents, therefore, are often used for their detec- 
tion and isolation. 

Only the more important alkaloids are described in the 
following pages. 

Alkaloids derived from Pyridine. 

Coniine, C 8 H 17 ]N;, one of the simplest known alkaloids, is 
contained in the seeds of the spotted hemlock (Conium 
maculatum), from which it may be prepared by distillation 
with soda. 

It is a colourless oil, boiling at 167, and is readily soluble 
in water ; it has a most penetrating odour, and turns brown 
on exposure to air. Coniine is a strong base, and com- 
bines with acids to form salts, such as the hydrochloride, 
C 8 H ir N,HCl, which are readily soluble in water; both the 
base and its salts are exceedingly poisonous, a few drops of 
the pure substance causing death in a short time by paralysing 
the muscles of respiration. 

* In cases of alkaloid poisoning it is usual, after using the stomach-pump, 
to wash out the stomach with dilute tannic acid, or to administer strong 
tea (which contains tannin), in order to render the alkaloids insoluble, and 
therefore harmless. 



502 ALKALOIDS. 

Ladenburg has shown that coniine is dextrorotatory a-propyl- 
piperidine, 

CH 2 



NH 

and has succeeded in preparing it synthetically, the first 
instance of the synthesis of an optically active alkaloid. 

a-Propylpiperidine contains an asymmetric carbon atom (shown 
in heavy type compare p. 544), and therefore, like lactic acid, it 
exists in three modifications ; the inactive modification, which is 
obtained by synthesis, may be resolved into its two optically active 
components by crystallisation of its tartrate (compare p. 557). 

Nicotine, C^H^l^, is present in the leaves of the tobacco- 
plant (Nicotiana tabacum), combined with malic or citric acid. 

Tobacco-leaves are extracted with boiling water, the extract 
concentrated, mixed with milk of lime, and distilled ; the distillate 
is acidified with oxalic acid, evaporated to a small bulk, decom- 
posed with potash, and the free nicotine extracted with ether. 
The- ethereal solution, on evaporation, deposits the crude alkaloid, 
which is purified by distillation in a stream of hydrogen. 

It is a colourless oil, which boils at 241, possesses a very 
pungent odour, and rapidly turns brown on exposure to air ; 
it is readily soluble in water and alcohol. It is a strong 
di-acid base, and forms crystalline salts, such as the hydro- 
chloride, C 10 H 14 N" 2 ,2HC1 ; it combines directly with two 
molecules of methyl iodide, yielding nicotine dimethiodide, 
C 10 H 14 N 2 ,2CH 3 I, a fact which shows that it is a di-tertiary 
base (p. 497). When oxidised with chromic acid it yields 
nicotinic acid (pyridine-/?-carboxylic acid, p. 492) ; it is, 
therefore, a pyridine-derivative, but its constitution cannot 
be fully discussed here. 

Nicotine is exceedingly poisonous, two or three drops taken 
into the stomach being sufficient to cause death in a few 
minutes. It shows no very characteristic reactions, but its 



ALKALOIDS. 503 

presence may be detected by its extremely pungent odour 
(which recalls that of a foul tobacco-pipe). 

Piperine, C 17 H 19 N0 3 , occurs to the extent of about 8-9 per 
cent, in pepper, especially in black pepper (Piper nigrum), 
from which it is easily extracted. 

The pepper is powdered and warmed with milk of lime for fifteen 
minutes ; the mixture is then evaporated to clryness on a water- 
bath, extracted with ether, the ethereal solution evaporated, and 
the residual crude pipeline purified by recrystallisation from alcohol. 

It crystallises in prisms, melts at 128, and is almost 
insoluble in water ; it is only a very weak base, and when 
heated with alcoholic potash it is decomposed into piperidine 
(p. 489) and piperic acid, 

C 17 H 19 N0 3 + H 2 = C 5 H U N + C 12 H 10 4 . 

Piperidine. Piperic Acid. 

Atropine, or daturine, C^H^NOg, does not occur in nature, 
although it is prepared from the deadly nightshade (Atropa 
belladonna). This plant contains two isomeric and closely 
related alkaloids, Tiyoscyamine and liyoscine, and the former 
readily undergoes intramolecular change into atropine on 
treatment with bases. 

The plant is pressed, the juice mixed with potash, and extracted 
with chloroform (1 litre of juice requires 4 grams of potash and 
30 grams of chloroform) ; the chloroform is then evaporated, the 
atropine extracted from the residue with dilute sulphuric acid, the 
solution treated with potassium carbonate, and the precipitated 
alkaloid recrystallised from alcohol. 

It crystallises from dilute alcohol in glistening prisms, and 
melts at 115; it is readily soluble in alcohol, ether, and 
chloroform, but almost insoluble in water. When boiled 
with baryta water it is readily hydrolysed, yielding tropic acid 
and a base called tropine, which is a derivative of piperidine, 



C 1Y H 23 N0 3 + H 2 = C 6 H 5 'CH< + C 8 H 16 NO. 



Tropic Acid. Tropine. 

Atropine is a strong base, and forms well-characterised salts, 



504 ALKALOIDS. 

of which the sulphate, (C l7 H 23 N0 3 ) 2 ,H 2 S0 4 , is readily soluble, 
and, therefore, most commonly used in medicine ; both the 
base and its salts are excessively poisonous, 0-05-0-2 gram 
causing death. Atropine sulphate is largely used in ophthal- 
mic surgery, owing to the remarkable property which it 
possesses of dilating the pupil when its solution is placed 
on the eye. 

Test for Atropine. If a trace of atropine be moistened 
with fuming nitric acid, and evaporated to dryness on a 
water-bath, it yields a yellow residue, which, on the addition 
of alcoholic potash, gives an intense violet solution, the 
colour gradually changing to red. 

Cocaine, C 1 i 7 H 21 N0 4 , and several other alkaloids of less 
importance, are contained in coca-leaves (ErytTiroxylon coca). 

The coca-leaves are extracted with hot water (80), the solution 
mixed with lead acetate (in order to precipitate tannin, &c.), 
filtered, and the lead in the filtrate precipitated with sodium 
sulphate ; the solution is then rendered alkaline with soda, the 
cocaine extracted with ether, and purified by recrystallisation 
from alcohol. 

Cocaine crystallises in colourless prisms, melts at 98, and 
is sparingly soluble in water; it forms well-characterised 
salts, of which the hydrochloride, C 17 H 2] N0 4 ,HC1, is most 
largely used in medicine. Cocaine is a very valuable local 
anaesthetic, and is used in minor surgical operations, as 
its local application takes away all sensation of pain ; it 
is, however, poisonous, one grain injected subcutaneously 
having been attended with fatal results. 

When heated with acids or alkalies, cocaine is readily 
hydrolysed with formation of benzoic acid, methyl alcohol, 
and ecgonine, 
C 17 H 21 N0 4 + 2H 2 = C 6 H 5 -COOH + CH 3 -OH + C 9 H 15 N0 3 . 

Alkaloids derived from Quinoline. 

Quinine, C 20 H 24 N 2 2 , cinch onine (see below), and several 
other allied alkaloids occur in all varieties of cinchona-bark, 



ALKALOIDS. 505 

some of which contain as much as 3 per cent, of quinine. 
The alkaloids are contained in the bark, combined with 
tannic and quinic acids.* 

The powdered bark is extracted with dilute sulphuric acid, and 
the solution of the sulphates precipitated with soda. The crude 
mixture of alkaloids thus obtained is dissolved in alcohol, the 
solution neutralised with sulphuric acid, and the sulphates which 
are deposited repeatedly recrystallised from water. Quinine sul- 
phate is the least soluble, and separates out first, the sulphates of 
cinchonine and the other alkaloids remaining in solution ; from 
the pure sulphate, quinine may be obtained as an amorphous 
powder by adding ammonia. 

Quinine crystallises with 3 mols. H 2 0, melts at 177 when 
anhydrous, and is only very sparingly soluble in water; it 
is only a feeble di-acid base, and generally forms hydrogen 
salts, such as the sulphate, (C 20 H 24 N 2 2 ) 2 ,H 2 S0 4 + 8H 2 ; 
many of its salts are soluble in water, and much used in 
medicine as tonics, and for lowering the temperature in cases 
of fever, &c. 

Quinine is a di-tertiary base, because it combines with methyl 
iodide to form quinine dimethiodide, C 20 H 24 N 2 2 ,(CH 3 I) 2 ; it 
is a derivative of quirioline, because on oxidation with chromic 
acid it yields quininic acid (methoxyquinoline-y-carboxylic 

acid), 

COOH 
>~\ ^ 

CHj 




N 

Quinine contains one methoxy-group, as has been demon- 
strated by Zeisel's method (p. 498), and it is a methoxy- 
cinchonine, because on oxidation it yields the methoxy- 
derivative of quinoline-y-carboxylic acid (see below). 

Tests for Quinine. If a solution of a salt of quinine be 

mixed with chlorine- or bromine-water, and then ammonia 

* Quinic add, C 6 H 7 (OH) 4 -COOH, crystallises in prisms, and melts at 

162. It is a derivative of benzoic acid, being, in fact, tetrahydroxy- 

hexahydrobenzoic acid. 



506 ALKALOIDS. 

added, a highly characteristic emerald-green colouration is 
produced ; quinine is also characterised by the fact that 
dilute solutions of its salts show a beautiful light-blue 
fluorescence. 

Cinchonine, C 19 H 22 N 2 0, accompanies quinine in almost 
all the cinchona-barks, and is present in some kinds (in 
the bark, Cinchona Huanaco) to the extent of 2-5 per cent. 

In order to prepare cinchonine, the mother-liquors from the 
crystals of quinine sulphate (see above) are treated with soda, 
and the precipitate dissolved in the smallest possible quantity of 
boiling alcohol ; the crude cinchonine, which separates on cooling, 
is further purified by converting into the sulphate, and crystallising 
this salt from water. 

Cinchonine crystallises in colourless prisms, melts at 255, 
and resembles quinine in ordinary properties ; its salts, for 
example, are antipyretics, but are much less active than 
those of quinine. 

Oxidising agents, such as nitric acid and potassium per- 
manganate, readily attack cinchonine, converting it into a 
variety of substances, one of the most important of which 
is cinchoninlc acid, or quinoline-y-carboxylic acid, 

COOH 




The formation of this acid proves that cinchonine is a 
quinoline-derivative. 

Strychnine, C 21 H 22 N 2 2 , and brucine, two highly poison- 
ous alkaloids, are contained in the seeds of Strychnos nux 
vomica and of Strychnos Ignatii (Ignatius' beans), but they 
are usually extracted from the former. 

Powdered nux vomica is boiled with dilute alcohol, the filtered 
solution evaporated to expel the alcohol, and treated with lead 
acetate to precipitate tannin, &c. The nitrate is then treated 
with hydrogen sulphide to precipitate the lead, and the filtered 
solution mixed with magnesia and allowed to stand. The pre- 



ALKALOIDS. 507 

cipitated alkaloids are separated, and warmed with a little 
alcohol, which dissolves out the brucine ; the residual strychnine 
is further purified by recrystallisation from alcohol. 

The alcoholic solution of the brucine which still contains 
strychnine is evaporated, and the residue dissolved in dilute 
acetic acid ; this solution is now evaporated to dry ness on a 
water-bath, during which process the strychnine acetate decom- 
poses, with loss of acetic acid and separation of the free base. 
The stable brucine acetate is dissolved again by adding water, the 
filtered solution treated with soda, and the precipitated brucine 
purified by recrystallisation from dilute alcohol. 

Strychnine crystallises in beautiful rhombic prisms, and 
melts at 284 ; although it is very sparingly soluble in water 
(1 part in 4000 at 15), its solution possesses an intensely 
bitter taste, and is very poisonous. Strychnine is, in fact, 
one of the most poisonous alkaloids, half a grain of the 
sulphate having caused death in twenty minutes. 

Although strychnine contains two atoms of nitrogen, it 
is, like brucine, only a mon-acid base, forming salts, such 
as the hydrochloride, C 21 H 22 N 2 2 ,HC1 ; many of the salts 
are soluble in water. It is a tertiary base, because it com- 
bines with methyl iodide to form strychnine methiodide, 
C 21 H 22 N 2 2 ,CH 3 I. 

When distilled with potash, strychnine yields, among other 
products, quinoline ; probably, therefore, it is a derivative of 
this base. 

Test for Strychnine. Strychnine is very readily detected, 
as it shows many characteristic reactions, of which the 
following is the most important : When a small quantity 
of powdered strychnine is placed in a porcelain basin, a 
little concentrated sulphuric acid added, and then a little 
powdered potassium dichromate dusted over the liquid, an 
intense violet solution, which gradually becomes bright-red, 
and then yellow, is produced. 

Brucine, C 23 H 26 N 2 4 , crystallises in colourless prisms, 
with 4 mols. H 2 0, and melts, when anhydrous, at 178. 
It is more readily soluble in water and in alcohol than 



508 ALKALOIDS. 

strychnine, and, although very poisonous, it is not nearly 
so deadly as the latter (its physiological effect being only 
about -^jth of that of strychnine). Although it contains 
two atoms of nitrogen, brucine, like strychnine, is a mon- 
acid base. The liydrochloride, for example, has the com- 
position C 23 H 26 N 2 4 ,HC1 ; it is also a tertiary base, because 
it combines with methyl iodide to form brucine methiodide, 
C 23 H 26 N 2 4 ,CH 3 L 

Test for Brucine. When a solution of a brucine salt is 
treated with nitric acid, a deep brownish-red colouration is 
obtained, and, on warming, the solution becomes yellow ; if 
now stannous chloride be added, an intense violet colouration 
is produced. 

This colour reaction serves as a delicate test, both for 
brucine and for nitric acid, as it may be carried out with 
very small quantities. 

Alkaloids contained in Opium. 

The juice of certain kinds of poppy-heads (Papaver som- 
niferum) contains a great variety of alkaloids, of which 
morphine is the most important, but code'ine, narcotine, 
thebdine, and papaverine may also be mentioned. All these 
compounds are present in the juice in combination with 
meconic acid* and partly also with sulphuric acid. When 
incisions are made in the poppy-heads, and the juice which 
exudes is collected and left to dry, it assumes a pasty con- 
sistency, and is called opium. An alcoholic tincture of 
opium, containing about 1 grain of opium in 15 minims, 
is known as laudanum. 

Preparation of Morphine. Opium is extracted with hot water, 
the extract boiled with milk of lime, and filtered from the pre- 
cipitate, which contains the meconic acid, and all the alkaloids, 

* Meconic acid, C 5 HO 2 (OH)(COOH) 2 , is a hydroxydicarboxylic acid be- 
longing to the aliphatic series. It crystallises with three molecules of 
water, and gives, with ferric chloride, an intense dark-red colouration. 
In cases of suspected opium -poisoning this acid is always tested for, owing 
to the ease with which it can he detected by this colour reaction. 



ALKALOIDS. 509 

except morphine. The filtrate is then concentrated, digested 
with ammonium chloride until ammonia ceases to be evolved (to 
convert any lime present into soluble calcium chloride), and allowed 
to stand for some days ; the morphine, which separates, is collected 
and purified by recrystallisation from fusel oil (Part I. p. 107). 

Morphine, C 17 H 19 N0 3 , crystallises in colourless prisms, 
with 1 mol. H 2 0, and is only slightly soluble in water 
and cold alcohol, but dissolves readily in potash and soda, 
from which it is reprecipitated on the addition of acids ; 
it has, in fact, the properties of a phenol. At the same 
time, it is a mon-acid base, and forms well-characterised 
salts with acids; the hydrochloride, C 17 H 19 N0 3 ,HC1 + 3H 2 0, 
crystallises from water in needles, and is the salt most 
commonly employed in medicine. Morphine is a tertiary 
base, and when treated with methyl iodide it yields morphine 
methiodide, C ir H 19 N0 3 ,CH 3 I. 

Morphine has a bitter taste, and is excessively poisonous, 
one grain of the hydrochloride having been found sufficient 
to cause death ; on the other hand, the system may become 
so accustomed to the habitual use of opium that, after a 
time, very large quantities may be taken daily without fatal 
effects. Morphine is extensively used in medicine as a 
soporific, especially in cases of intense pain. 

Tests for Morphine. Morphine has the property of liberat- 
ing iodine from a solution of iodic acid. If a little iodic 
acid be dissolved in water, and a few drops of a solution 
of morphine hydrochloride added, a brownish colouration 
is at once produced, owing to the liberation of iodine, 
and on adding some of the solution to starch-paste, the 
well-known deep-blue colouration is obtained. 

A solution of morphine, or of a morphine salt, gives a 
deep -blue colouration with ferric chloride, but perhaps 
the most delicate test for the alkaloid is the following : 
If a trace of morphine be dissolved in concentrated sulphuric 
acid, the solution kept for 15 hours, and then treated with 
nitric acid, it gives a bluish-violet colour, which changes 



510 ALKALOIDS. 

to blood-red. This reaction is very delicate, and is well 
shown by 0-01 milligramme of morphine. 

Morphine contains two hydroxyl-groups, one of which is phenolic, 
the other alcoholic ; it is to the presence of the phenolic hydroxyl- 
group that morphine owes its property of dissolving in alkalies, 
and giving a blue colour with ferric chloride. 

If the base be heated with potash and methyl iodide, methyl- 
morphine, C 17 H 17 NO(OCH 3 )-OH, is produced, a substance which is 
identical with codeine, an alkaloid which accompanies morphine 
in opium. Codeine is insoluble in alkalies, and is, therefore, not 
a phenol; it behaves, however, like an alcohol, and gives, with 
acetic anhydride, acetylcode'ine, C 17 H] 7 NO(OCH 3 )-C 2 H 3 O 2 . 

It is very remarkable that morphine seems to be a derivative 
of phenanthrene, as derivatives of this hydrocarbon are very 
seldom met with in nature. If morphine be distilled with zinc- 
dust, a considerable quantity of this hydrocarbon is obtained, 
together with pyridine, quinoline, and other substances. 

Alkaloids related to Uric Acid. 

Caffeine, theine, or methyltheobromine, C 8 H 10 N 4 2 , occurs 
in coffee-beans (J per cent.), in tea (2 to 4 per cent.), in 
kola-nuts (2-5 per cent.), and in other vegetable products. 

Tea (1 part) is macerated with hot water (4 parts), milk of lime 
(1 part) added, and the whole evaporated to dry ness on a water- 
bath ; the caffeine is then extracted from the residue by means of 
chloroform, the extract evaporated, and the crude base purified by 
recrystallisation from water. 

Caffeine crystallises in long, colourless needles, with 1 mol. 
H 2 0, melts at 225, and at higher temperatures sublimes un- 
decomposed ; it has a bitter taste, and is sparingly soluble 
in cold water and alcohol. Caffeine is a feeble base, and 
forms salts only with strong acids ; the hydrochloride, 
C 8 H 10 ]\ T 4 2 ,HC1, is at once decomposed on treatment with 
water, with separation of the base. 

The constitution of caffeine has been determined by E. 
Fischer, who has shown that this substance and uric acid are 
very closely allied. 

Tests for Caffeine. If a trace of caffeine be evaporated with 
concentrated nitric acid, it gives a yellow residue (amalinic 



ALKALOIDS. 511 

acid), which on the addition of ammonia becomes intensely 
violet (murexide reaction) ; this reaction is also shown by 
uric acid (Part I. p. 303). A solution of caffeine in chlorine 
water yields, on evaporation, a yellowish-brown residue, 
which dissolves in dilute ammonia, with a beautiful violet- 
red colouration. 

Theobromine, C 7 H 8 N 4 O 2 , occurs in cocoa-beans, from which it 
may be obtained by treatment with lime, and extraction with 
alcohol. It crystallises from water, and shows the greatest resem- 
blance to caffeine in properties ; the latter is, in fact, methyltheo- 
bromine, and may be obtained directly from theobromine in the 
following way : 

Theobromine contains an ^>NH group, the hydrogen of which is 
readily displaced by metals (as in succinimide, Part I. p. 243), and 
when treated with an ammoniacal silver nitrate solution it yields 
silver theobromine. This substance interacts readily with methyl 
iodide with formation of caffeine, 

C 7 H 7 N 4 O 2 Ag + CH 3 I = C 7 H 7 N 4 O 2 -CH 3 + Agl. 

Silver Theobromine. Caffeine. 

The relationship between uric acid, theobromine, and caffeine is 
expressed by the following graphic formulae, 

/NH-CO-C-NH, /NH . CO C-N (CHA 
C0< >CO C0< || >CH 

\NH C-NH/ \N(CH 3 ) C 1 

Uric Acid. Theobromine. 

,N(CH 3 ).CO.C.N(CH 3 k 

II >CH 

s N(C H 3 ) C 

Caffeine. 



co<; 



Antipyrine, C 11 H 12 N 2 0, does not occur in nature, and is 
briefly described here as an example of what may be termed 
an ' artificial alkaloid ; ' it was first obtained by Knorr by 
treating ethyl acetoacetate (Part I. p. 193) with phenyl- 
hydrazine (p. 388), and then heating the product (plienyl- 
metliylpyrazolone) with methyl iodide, 

C 6 H 10 3 + C 6 H 5 .NH.KE 2 = C 10 H 10 N 2 + C 2 H 5 .QH + H 2 

C 10 H 10 N 2 + CH 3 I = C n H 12 N" 2 0,HI. 

It is a colourless, crystalline compound, melts at 1 1 3, and is 
readily soluble in water and alcohol ; it is a strong mon-acid 



512 ALKALOIDS. 

base, and its salts dissolve freely in water. Its aqueous solu- 
tion gives a deep-red colouration with ferric chloride, and a 
bluish-green colouration with nitrous acid. Antipyrine is 
employed in medicine, as a substitute for quinine, for lower- 
ing the body temperature in cases of fever. 

Antifebrin, or acetanilide, another important febrifuge, has 
already been described (p. 374). 

CJioline, Betaine, Neurine, and Taurine. 

Certain nitrogenous substances which occur in the animal 
kingdom may also be referred to in this chapter, because they 
are basic compounds of great physiological importance ; they 
really belong, however, to different classes of the fatty series. 

Choline, or hydroxyethyltrimethylammonium hydroxide, 
OH.CH 2 .CH 2 .N(CH 3 ) 3 .OH, occurs in the blood, bile, brain- 
substance, yolk of egg, and in other parts of animal organisms, 
usually in the form of lecithin (a compound of choline, 
glycerol, phosphoric acid, and various fatty acids) ; it also 
occurs in mustard and in hops. It may be prepared syntheti- 
cally by warming trimethylamine with ethylene oxide in 
aqueous solution, 

N(CH 8 ) 8 + C 2 H 4 + H 2 = C 5 H 15 N0 2 . 

It is a crystalline, very hygroscopic, strongly basic substance, 
its aqueous solution having an alkaline reaction, and absorb- 
ing carbon dioxide from the air ; with hydrochloric acid it 
yields the corresponding chloride, OH-CH 2 -CH 2 -N(CH 3 ) 3 C1, 
but when boiled with water it is decomposed into glycol and 
trimethylamine. 

Betaine, C 5 H n N0 2 , is formed when choline undergoes mild 
oxidation ; the acid, which is first produced by the conversion 
of the -CH 2 -OH group into carboxyl, 



loses one molecule of water, forming betaine, 



ALKALOIDS. 513 

salt-like compound, which has a neutral reaction, a somewhat 
sweet taste, and crystallises from dilute alcohol with 1 mol. 
H 2 0. 

When treated with hydrochloric acid, betame is converted 
into the chloride, COOH-CH 2 .N(CH 3 ) 3 C1, and this compound 
may also be obtained synthetically by heating trimethylamine 
with chloracetic acid. Betaine occurs in beet-juice, and is 
present in large quantities in the mother-liquors obtained in 
the preparation of beet-sugar. 

Neurine, CH 2 :CH-N(CH 3 ) 3 -OH (vmyltrimethylammonium 
hydroxide), can be obtained by heating choline with hydriodic 
acid, and then treating the product with silver hydroxide, 

CH 2 LCH 2 .N(CH 3 ) 3 I + 2AgOH = 

CH 2 :CH.N(CH 3 ) 3 .OH + 2AgI + H 2 ; 

it is formed, together with choline and numerous other bases, 
during the putrefaction of animal albuminoid matter."* 

Neurine is only known in solution as a strongly basic, very 
soluble, and exceedingly poisonous substance, but some of its 
salts, as, for example, the chl&ride, CH 2 :CH.N(CH 3 ) 3 C1, are 
crystalline. 

Taurine, or amidoethylsulphonic acid, NH 2 -CH 2 .CH 2 -S0 3 H, 
occurs in the combined state in ox-gall and in many other 
animal secretions. It crystallises in colourless prisms, melts 
and decomposes at about 240, and is readily soluble in water, 
but insoluble in alcohol; it has a neutral reaction, and is 
only a feeble acid, because the presence of the amido-group 
neutralises the effect of the sulphonic group to such an extent 
that it forms salts only with strong bases. When treated 
with nitrous acid, the amido-group is displaced by hydroxyl, 
just as in the case of primary amines, and hydroxyethyl- 
sulphonic acid (isethionic acid) is formed, 

NH 2 CH 2 -CH 2 S0 3 H + HO NO = OH CH. 2 CH 2 SO 3 H + N 2 + H 2 O. 

* The bases produced during the putrefaction of animal albuminoid 
matter are known collectively as ptomaines, and many of them are highly 
poisonous. 

Or. Chem. 2 G 



514 DYES AND THEIR APPLICATION. 

CHAPTER XXXV. 

DYES AND THEIR APPLICATION. 

Although most organic compounds are colourless, some, 
especially certain classes of the aromatic series, are intensely 
coloured substances amongst which representatives of almost 
every shade occur; most of the principal dyes used at the 
present day are, in fact, aromatic compounds, the primary 
source of which is coal-tar hence the well-known expression 
* coal-tar colours.' 

That a dye must be a coloured substance is, of course, 
obvious, but a coloured substance is not necessarily a dye, in 
the ordinary sense of the word, unless it is also capable of 
fixing itself, or of being fixed, in the fabric to be dyed, in 
such a way that the colour is not removed by rubbing or by 
washing with water ; azobenzene, for example, is intensely 
coloured, but it would not be spoken of as a dye, because it 
does not fulfil the second condition. 

Again, if a piece of silk or wool be dipped into a solution of 
picric acid it is dyed yellow, and the colour is not removed 
on subsequently washing with water, but is fixed in the fibre. 
If, however, a piece of calico or other cotton material be 
treated in the same way, the picric acid does not fix itself, 
but may be removed by washing with water. A given 
substance may, therefore, be a dye for certain materials, but 
not for others ; the animal fabrics, silk and wool, fix picric 
acid, and are dyed by it, but the vegetable fabric, cotton, 
does not a behaviour which is repeatedly met with in the 
case of other colouring matters. 

Now, since picric acid is soluble in water, it is evident that 
it must have undergone some change when brought into 
contact with the silk or wool, otherwise it would be dissolved 
out of the fabric on washing with water. Materials such as 



DYES AND THEIR APPLICATION. 515 

wool, cotton, silk, &c., consist of minute fibres, which may 
be very roughly described as long, cylindrical, or flattened 
tubes (except in the case of silk, the fibres of which are 
solid), the walls of which, like parchment paper and animal 
membrane, allow of the passage of water and of dissolved 
crystalloids by diffusion, but not that of colloid substances, 
or, of course, of matter in suspension. If, therefore, the picric 
acid were present in the fibre, as picric acid, it would, on wash- 
ing, rapidly pass into the water by diffusion ; as this is not the 
case, it must be assumed that it has actually combined with 
some substance in the silk or wool, and has been converted 
into a yellow compound, which is either insoluble or a colloid. 

The nature of the insoluble compound formed when a material is 
dyed in this way is not known, but there are reasons for supposing 
that certain constituents of the fibre unite with the dye to form 
an insoluble salt. This seems probable, from the fact that nearly 
all dyes which thus fix themselves directly on the fabric are, to 
some extent, either basic or acid in character. Azobenzene, as 
already mentioned, is not a dye, probably, because it is a neutral 
substance ; if, however, some group, such as an amido-, liydroxyl-, 
or sulphonic-group, which confers basic or acid properties, be intro- 
duced into the molecule of azobenzene, then the resulting deriva- 
tive is a dye, because it bas the property of combining directly with 
the fibres of certain materials. 

Another fact Avhich leads to the same conclusion may be quoted. 
Certain dyes as, for example, rosaniline are salts of bases which 
are themselves colourless, and yet some materials may be dyed 
simply by immersion in colourless solutions of these bases, the 
same colour being obtained as with the coloured salt (that is, 
the dye itself) ; this can only be explained by assuming that 
some constituent of the fibre combines with the colourless base, 
forming with it a salt of the same colour as the dye. 

Some fibres, especially silk and wool, seem to contain both acid 
and basic constituents, as they are often dyed directly both by 
basic and by acid dyes ; cotton, on the other hand, seems to be 
almost free from both, as, except in rare cases, it does not combine 
witli colouring matters. 

Granting, then, that the fixing of a dye within the fibre is 
the result of its conversion into some insoluble compound, 



516 DYES AND THEIR APPLICATION. 

it seems reasonable to suppose that, even if a colouring 
matter be incapable of fixing itself in the fibre of the material, 
it might still be employed as a dye, provided that, after it 
had once passed through the walls of the fibre, it could be 
there converted into some insoluble compound by other 
means ; this principle is applied in the case of many dyes, 
and the substances used to fix them in the material are termed 
mordants. 

Dyes, therefore, may be roughly divided into two classes with 
respect to their behaviour with a given fabric : (a) Those 
which fix themselves on the fabric, and (b) those which do 
so only with the aid of a mordant. 

Mordants are substances which (usually after first under- 
going some preliminary change) combine with dyes, forming 
insoluble coloured compounds ; the colour of the dyed fabric 
in such cases depends, of course, on that of the compound 
thus produced, and not on that of the dye itself, so that 
by using different mordants, different shades or colours are 
often obtained. 

As an example of dyes of the second class, alizarin may 
be taken, as it illustrates very clearly the use of mordants. 

If a piece of calico be dipped into an aqueous solution of 
alizarin it is coloured yellow, but the colour is not fixed, and 
is easily got rid of on washing with soap and water ; if, how- 
ever, a piece of calico which has been previously mordanted 
with a suitable aluminium salt (in the manner described 
below) be treated in the same way, it is dyed a fast red, the 
alizarin having combined with the aluminium compound in 
the fibre to form a red insoluble substance ; if, again, the 
calico had been mordanted with a ferric salt instead, it would 
have been dyed a fast dark purple* 

Substances very frequently employed as mordants are 
certain salts of iron, aluminium, chromium, and tin, more 

* A colouring matter such as alizarin, which can thus be used for the 
production of different colours, is sometimes termed ' polygenetic ; ' a dye 
which gives only one colour is then named ' monogenetic.' 



DYES AND THEIR APPLICATION. 517 

especially those, such as the acetates, thiocyanates, and alums, 
which undergo decomposition on treatment with water or 
with steam, yielding either an insoluble metallic hydroxide 
or an insoluble basic salt. 

The process of mordanting usually involves two operations : 
firstly, the fabric is passed through, or soaked in, a solution 
of the mordant, in order that its fibres may become impreg- 
nated with the metallic salt ; secondly, the fabric is treated 
in such a way that the salt is decomposed within the fibres, 
and there converted into some insoluble compound. 

The second operation, the fixing of the mordant so that it 
will not be washed out when the fabric is brought into the 
dye-bath, is accomplished in many ways. One of the simplest 
is to pass the mordanted material through a solution of some 
weak alkali (ammonia, sodium carbonate, lime) or of some 
salt, such as sodium phosphate or arsenate, which interacts 
with the metallic salt in the fibre, forming an insoluble 
metallic hydroxide, phosphate, arsenate, &c. Another method, 
applicable more especially in the case of mordants which are 
salts of volatile acids, consists in exposing the fabric to the 
action of steam, at a suitable temperature ; under these con- 
ditions the metallic salt dissociates, the acid volatilises with 
the steam, and an insoluble hydroxide or basic salt remains in 
the fibre. 

In the case of silk and woollen fabrics, the operations of 
mordanting and fixing the mordant may often be carried out 
simultaneously, by merely soaking the materials in a boiling 
dilute solution of the mordant ; under these conditions the 
metallic salt is partially dissociated, and deposited in the 
fibre in an insoluble form ; silk may sometimes be simply 
soaked in a cold, concentrated solution of the mordant, and 
then washed with water to cause the dissociation of the 
metallic salt. 

In cases where only parts of the fabric are to be dyed, as, 
for example, in calico-printing, a solution of a suitable mor- 
dant may be mixed with the dye, and with some thickening 



518 DYES AND THEIR APPLICATION. 

substance, such as starch, dextrin, gum, &c., and printed on 
the fabric in the required manner, the thickening being 
used to prevent the mordant spreading to other parts; the 
material is then submitted to a steaming process, when the 
metallic hydroxide which is produced combines with and 
fixes the dye. 

All these processes are identical in principle, the object 
being to deposit some insoluble metallic compound within the 
fibre ; when, now, the mordanted material is treated with a 
solution of a suitable dye, the latter unites with the metallic 
hydroxide, forming a coloured compound which is fixed in 
the fibre. The coloured substances produced by the combina- 
tion of a dye with a metallic hydroxide are termed lakes, and 
those dyes which form lakes are called acid dyes. 

Tannin (p. 453) is an example of a different class of 
mordants namely, of those which are employed with basic 
dyes, such as malachite green (p. 521) and rosaniline (p. 525) : 
its use depends on the fact that, being an acid, it combines 
with dyes of a basic character, forming with them insoluble 
coloured salts (tannates), which are thus fixed in the fibre. 
The fabric is mordanted by first passing it through a solution 
of tannin, and then through a weak solution of tartar emetic, 
or stannic chloride, which converts the tannin into an in- 
soluble antimony or tin tannate, and thus fixes it in the fibre. 

All colouring matters are converted into colourless com- 
pounds on reduction ; in the case of some dyes, the reduction 
product cannot be directly reconverted into the dye by oxida- 
tion, as, for example, in that of amidoazobenzene, which, 
when treated with powerful reducing agents, yields aniline 
and ^-phenylenediamine, 

C 6 H 5 .N:N.C 6 H 4 .NH 2 + 4H = C 6 H 5 -NH 2 + NH 2 -C 6 H 4 .ISrH 2 . 

When, however, the colourless reduction product differs 
from the dye in such a way that it may be readily recon- 
verted into the dye by oxidising agents, the reduction product 
is called a leuco-compound. 



DYES AND THEIR APPLICATION. 519 

Amidoazobenzene, for example, the hydrochloride or oxalate 
of which is the dye aniline yellow (p. 535), on treatment with 
mild reducing agents, such as zinc-dust and acetic acid, yields 
amidohydrazobenzene, which is only slightly coloured, 

C G H 5 .N:N.C 6 H 4 .NH 2 + 2H - C 6 H 5 .NH.NH.C 6 H 4 -NH 2 . 

The last-named substance is readily oxidised to amidoazo- 
benzene on shaking its alcoholic solution with precipitated 
(yellow) mercuric oxide, and is, therefore, /ewco-amidoazo- 
benzene ; many examples of leuco-compounds will be met 
with in the following pages. 

When an insoluble dye yields a soluble leuco-compound, 
which is very readily reconverted into the dye on oxidation, 
it may be applied to fabrics in a special manner, as, for 
example, in the case of indigo-blue. Indigo-blue, C 16 H 10 N 2 2 
(p. 539), is insoluble in water, but on reduction it is converted 
into a readily soluble leuco-compound, C 16 H 12 N" 2 2 , known as 
indigo-white : in dyeing with indigo, a solution of indigo- 
white is prepared by reducing indigo, suspended in water, 
with grape-sugar and sodium hydroxide, or ferrous sulphate 
and sodium hydroxide, and the fabric is then passed through 
this solution, whereupon the indigo-white diffuses through 
the walls into the fibres; on subsequent exposure to the air 
the indigo-white is reconverted into indigo-blue by oxidation, 
and the insoluble dye is thus fixed in the fabric. 

Some of the more important dyes will now be described : 
as, however, it would be impossible to discuss fully the 
constitutions of these compounds, it must be understood that 
the formulae employed in the following pages are those 
commonly accepted, and that most of them have been satis- 
factorily established. 

Derivatives of Triphenylmethane. 

Triphenylmethane, C 6 H 5 -CH(C 6 H 5 ) 2 (p. 351), or, more 
strictly speaking, triphenyl carbiriol, C 6 H 5 -C(C 6 H 5 ) 2 -OH, is 
the parent substance of a number of dyes, which are of very 



520 DYES AND THEIR APPLICATION. 

great technical importance on account of their brilliancy ; 
as examples, malachite green, pararosaniline, and rosaniline 
may be described. 

Three distinct classes of substances are constantly met 
with in studying the triphenylmethane group of colouring 
matters namely, the leuco-base, the colour-base, and the 
dye itself. 

The leuco-base (p. 518) is an amido-derivative of triphenyl- 
methane ; in the case of malachite green, for example, the 
leuco-base is tetramethyldiamidotriphenylmethane, 



The colour-base is an amido-derivative of triphenyl carbinol, 
and is produced from the leuco-base by oxidation, just as 
triphenyl carbinol results from the oxidation of triphenyl- 
methane (p. 351); the colour-base of malachite green, for 
example, is tetramethyldiamidotriphenyl carbinol, 



Both the leuco-base and the colour-base are usually colour- 
less, and the latter also yields colourless, or only slightly 
coloured, salts on treatment with cold acids ; when warmed 
with acids, however, the colour-base gives highly coloured 
salts, which constitute the dye, water being eliminated, 
C 23 H 26 N" 2 + HC1 = C 23 H 25 N 2 C1 + H 2 0. 

Malachite Green Base. Chloride of Malachite Green. 

This loss of water is probably due to combination taking 
place between the hydroxyl-group and the hydrogen atom of 
the acid employed, and the conversion of the colourless into 
the coloured salt may be expressed as follows, 



This change namely, the elimination of two univalent 
atoms or groups resembles the conversion of colourless 
hydroquinone into highly coloured quinone (p. 426), and also 



DYES AND THEIR APPLICATION. 521 

that of ^-amidophenol into quinone-chlorimide (p. 428), and 
may be represented in a similar manner, 
C 6 H 5 .C(OH).C 6 H 4 .N(CH 3 ) 2 





(CH 3 ) 2 N, HC1 (CH 3 ) 2 NC1 

Hydrochloride of Colour-base. Chloride of Malachite Green. 

Exactly similar changes may be assumed to take place in the 
formation of the pararosaniline and rosaniline dyes, and, in 
fact, most colouring matters may be regarded as derivatives 
of quinones. 

Malachite green (of commerce) is a double salt, formed by 
the combination of the chloride of tetramethyldiamidotriphenyl 
carbinol with zinc chloride, and the first step in its manu- 
facture is the preparation of leaco-malacliite green or tetra- 

/~i TT 

methyl-p-diamidotriphenylmethane, C 6 H 6 -CH< r , 6 4 



Leuco-malachite green is manufactured by heating a mix- 
ture of benzaldehyde (1 mol.) and dimethylaniline (2 mols.) 
with hydrochloric acid, 

r< TT 
C 6 H 5 

It is a colourless, crystalline substance, which, when treated 
with oxidising agents, such as manganese dioxide and sul- 
phuric acid, or lead dioxide and hydrochloric acid, yields 
tetrametTiyldiamidotriplienyl carbinol, just as triphenylmethane, 
under similar circumstances, yields triphenyl carbinol, 

() p TT 

C 6 H 5 - 

This oxidation product is a colourless base, and dissolves 
in cold acids, yielding colourless solutions of its salts ; when, 
however, such solutions are warmed, the colourless salts lose 
one molecule of water, intensely green solutions being 



522 DYES AND THEIR APPLICATION. 

obtained; the formation of the chloride, for example, is 
expressed by the equation, 

C 23 H 26 N 2 + HC1 = C 28 H 26 N 2 C1 + H 2 0, 

and its double salt with zinc chloride (or the oxalate of the 
base), constitutes the malachite green (Victoria green, benzal- 
dehyde green) of commerce. 

Preparation of Malachite Green. Dimethylaniline (10 parts) and 
benzaldehyde (4 parts) are heated with zinc chloride (4 parts) in a 
porcelain basin or enamelled iron pot for two days at 100, with 
constant stirring ; the product is then submitted to distillation in 
steam, to get rid of the unchanged dimethylaniline, and after cool- 
ing, the insoluble leuco-compound is separated. This product is 
washed with water, dissolved in as little hydrochloric acid as 
possible, the solution diluted considerably, and the calculated 
quantity of freshly precipitated lead dioxide added. The filtered 
dark-green solution is then mixed with sodium sulphate, to precipi- 
tate any lead, again filtered, and the colouring matter precipitated 
in the form of its zinc double salt, 3C23H 25 N 2 Cl,2ZnCl 2 + 2H 2 0, by 
the addition of zinc chloride and common salt ; this salt is finally 
purified by recrystallisation. 

Malachite green, and other salts of the base, such as the 
oxalate, 2C 23 H 24 N 2 ,3C 2 H 2 4 , form deep-green crystals, and 
are readily soluble in water ; they are decomposed by alkalies, 
with separation of the colour-base, tetramethyldiamidotri- 
phenyl carbinol. 

Malachite green dyes silk and wool directly an intense 
dark-bluish green, but cotton must first be mordanted with 
tannin and tartar emetic (p. 518), and then dyed in a bath 
gradually raised to 60. 

Many other dyes, closely allied to malachite green, are prepared 
by condensing benzaldehyde with tertiary alkylanilines (p. 377). 
Brilliant green, for example, is finally obtained when diethyl- 
aniline is employed instead of dimethylaniline in the above- 
described process, whereas acid green is obtained from benzal- 
dehyde and ethylbenzylaniline,* C 6 H 5 -N(C 2 H 5 )-C 7 H 7 , in a similar 
manner. The salts of these two colouring matters are very 
sparingly soluble in water, and therefore of little use as dyes ; 

* Produced by treating aniline with benzylchloride and ethyl bromide 
successively. 



t>YES AND THEIR APPLICATION. 523 

for this reason, the bases are treated with anhydrosulphuric acid, 
and thus converted into a mixture of readily soluble sulphonic 
acids, the sodium salts of which constitute the commercial dyes. 
Silk and wool are dyed in a bath acidified with sulphuric acid 
(hence the name acid green), and very bright greens are obtained, 
but these dyes are not suitable for cotton. 

Pararosaniline and rosaniline are exceedingly important 
dyes, which, like malachite green, are derived from triphenyl- 
methane. Whereas, however, malachite green is a derivative 
of <imf/i?'cfo-triphenylmethane, the rosanilines are all triamido- 
triphenylmethane derivatives, as will be seen from the follow- 
ing formulae, 



Triphenyhnethane. Tolyldiplienylmethane 

(Methyl triphenylmethane). 



Leuco-pararosaniline Leuco-rosaniline 

(Paraleucaniline). (Leucaniline). 

Triamiclotriphenylmetliane. Triamidotolyldiphenylmethane. 



Pararosaniline Base. Rosaniline Base. 

Triamidotriphenyl Carbinol. Triamidotolyldiphenyl Carbinol. 



Pararosaniline Chloride. Rosaniline Chloride. 

In all these compounds the amido-groups are in the para- 
position to the methane carbon atom. 

Pararosaniline (of commerce) is the chloride of triamido- 
triphenyl carbinol, a base which is most conveniently pre- 
pared by oxidising a mixture of >-toluidine (1 mol.) and 
aniline (2 mols.) with arsenic acid, or nitrobenzene (compare 
rosaniline, p. 525), 



+ 2H0. 



524 DYES AND THEIR APPLICATION. 

Probably the jo-toluidine is first oxidised to jo-amidobenzaldehyde, 
NH 2 'C 6 H 4 -CHO, which then condenses with the aniline (as in the 
case of the formation of leuco-malachite green) to form leuco-para- 
rosaniline ; this compound is then converted into the pararosaniline 
base by further oxidation. 

The salts of pararosaniline have a deep-magenta colour, and 
are soluble in warm water ; they dye silk, wool, and cotton, 
under the same conditions as described in the case of 
malachite green ; pararosaniline is, however, not so largely 
used as rosaniline. 

Triamidotriphenyl carbinol, the pararosaniline colour-base, 
is obtained, as a colourless precipitate, on adding alkalies to a 
solution of the chloride, or of some other salt : it crystallises 
from alcohol in colourless needles, and, when treated with 
acids, gives the intensely coloured pararosaniline salts. 

Leuco-pararosaniline, paralencaniline or triamidotriphenyl- 
methane, NH 2 -C 6 H 4 -CH(C 6 H 4 -NH 2 ) 2 , is prepared by reducing 
triamidotriphenyl carbinol with zinc-dust and hydrochloric acid, 
NH 9 .C 6 H 4 -C(OH)(C 6 H 4 .NH 2 ) 2 + 2H = 

NH 2 -C 6 H 4 .CH(C 6 H 4 .]S T H 2 ) 2 + H 2 0. 

It crystallises in colourless plates, melts at 148, and forms 
salts, such as the hydrochloride, C 19 H 19 N 3 ,3HC1, with three 
equivalents of an acid. When the hydrochloride is treated 
with nitrous acid it is converted into a tri-diazo-compound, 
CH(C 6 H 4 -N 2 C1) 3 , which, when boiled with water, yields 
aurin, C 19 H 14 3 (p. 530), and when heated with alcohol, is 
converted into triphenylmethane, just as diazobenzene chloride, 
under similar conditions, yields phenol or benzene. 

Constitution of Pararosaniline. Since triphenylmethane 
can be obtained from pararosaniline in this way, the latter 
is a derivative of this hydrocarbon (an important fact, 
first established by E. and 0. Fischer in 1878); moreover, 
pararosaniline may be prepared from triphenylmethane, as 
follows : Triphenylmethane is converted into trinitrotriphenyl- 
methane, jS"0 2 'C 6 H 4 -CH(C 6 H 4 -N0 2 ) 2 a compound in which 
it has been shown that all the nitro-groups are in the 



DYES AND THEIR APPLICATION. 525 

^-position to the methane carbon atom with the aid of 
fuming nitric acid ; this nitre-compound, on reduction, yields 
a substance which is identical with leuco-pararosaniline, and 
which, on oxidation, is readily converted into the colour- 
base, triamidotriphenyl carbinol ; this base, when treated 
with acids, yields salts of pararosaniline, with elimination 
of water, 



HC1,NH 2 -C 6 H 4 .< 

v < 

Hydrochloride of Pararosaniline 



Chloride of Pararosaniline. 

Eosaniline (of commerce), fuchsine, or magenta, is the 
chloride (or acetate) of triamidotolyldiphenyl carbinol, a base 
which is produced by the oxidation of equal molecular pro- 
portions of aniline, o-toluidine, and j>toluidine (with nitro- 
benzene, arsenic acid, mercuric nitrate, &c.), the reaction 
being similar in all respects to the formation of the para- 
rosaniline base from aniline (2 mols.) and ^-toluidine (1 mol.), 

o-Toluidine. 



TSJTT P TT PTT 4- 6432 , Qf) - 

H 2' C 6 H 4' CH 3 + c 6 H 5 .NH 2 

p-Toluidine. Aniline. 

NH 2 -C A-qOHK^J^' + 2H 2 0. 

Kosaniline Base. 

Rosaniline is usually manufactured at the present time by 
what is termed the ' nitrobenzene process,' or the 'arsenic 
acid process. 1 

To the requisite mixture of aniline, o-toluidine, and ^-toluicline* 
(38 parts), hydrochloric acid (20 parts) and nitrobenzene (20 parts) 
are added, and the whole is gradually heated to 190, small quan- 
tities of iron-filings (3-5 parts) being added from time to time 
(see below). At the end of five hours the reaction is complete, 

* Crude 'aniline-oil,' a mixture of these three bases, has sometimes been 
used instead of the pure compounds. 



526 DYES AND THEIR APPLICATION. 

and steam is then led through the mass to drive off any unchanged 
aniline, toluidine, or nitrobenzene, after which the residue is pow- 
dered and extracted with boiling water, under pressure; lastly, 
the extract is mixed with salt, and the crude rosaniline chloride 
which separates purified by recrystallisation. 

In this reaction the nitrobenzene acts only indirectly as the 
oxidising agent ; the ferrous chloride, produced by the action of 
the hydrochloric acid on the iron, is oxidised by the nitrobenzene 
to ferric chloride, which in its turn oxidises the mixture of aniline 
and toluidines to rosaniline, and is itself again reduced to ferrous 
chloride; the action is therefore continuous, and only a small 
quantity of iron is necessary. 

The salts of the rosaniline base with one equivalent of 
acid, as, for example, the chloride, C 20 H 20 N 3 C1, form magni- 
ficent crystals, which show an intense green metallic lustre ; 
they dissolve in warm water, forming deep-red solutions, 
and dye silk, wool, and cotton a brilliant magenta colour, 
the conditions of dyeing being the same as in the case of 
malachite green. 

The addition of alkalies to the saturated solution of the 
chloride of rosaniline destroys the colour, and causes the 
precipitation of the colour-base, triamidotolyldiphenyl car- 
binoly C 2( fL 2() N B -0~H. (p. 523), which crystallises in colourless 
needles, and on warming with acids is at once reconverted 
into the intensely coloured salts. When reduced with tin 
and hydrochloric acid, the rosaniline salts yield leuco-ros- 
aniline, C 20 H 21 N 3 (p. 523), a colourless, crystalline substance, 
which, when treated with oxidising agents, is again converted 
into rosaniline. 

The constitution of rosaniline has been deduced in the 
same way as that of pararosaniline (p. 524), since, by means 
of the diazo-reaction, leuco-rosaniline has been converted 
into diphenyl-m-tolylmethane, CH 3 -C 6 H 4 -CH(C 6 H 5 ) 2 ; leuco- 
rosaniline has, therefore, the constitution, 

(3) CH (i> /CH.NH (4) 



and the rosaniline salts are derived from this base, just as 



DYES AND THEIR APPLICATION. 527 

those of pararosaniline and of malachite green are derived from 
leuco-pararosaniline and leuco-malachite green respectively. 

Derivatives of Pararosaniline and Rosaniline. 
The hydrogen atoms of the three amido-groups in pararos- 
aniline and rosaniline may be displaced by methyl- or ethyl- 
groups, by heating the dye with methyl or ethyl iodide 
(chloride or bromide) ; under these conditions tri-alkyl 
substitution products are obtained as primary products, one 
of the hydrogen atoms of each of the amido-groups being 
displaced. When, for example, rosaniline is heated with 
methyl chloride, it yields, in the first place, the chloride 
of 



64: NH(CH 8 )C1. 



PTT ATTT 

633 : 8 

This compound is a reddish-violet dye; the corresponding 
triethyl-TossLmline chloride is the principal constituent of 
Hofmann's violet, dahlia, primula, &c. dyes, which have now 
been superseded by more brilliant violets. 

By the continued action of methyl iodide on rosaniline, 
the iodide of tetramethyl-iossimlme is obtained. This sub- 
stance is a magnificent, bluish-violet dye, but is now little 
used ; it is a tertiary base, and, like dimethylaniline, it 
combines directly with methyl iodide, forming an additive 
compound of the composition, C 20 H 16 N 3 (CH 3 ) 4 I,CH 3 I + H 2 0, 
which, curiously enough, is green, and was formerly used 
under the name ' iodine green.' 

Starting, then, from rosaniline, which is a brilliant red 
dye, and substituting methyl-groups for hydrogen, the colour 
first becomes reddish-violet, and then bluish-violet, as the 
number of alkyl-groups increases. This change is more 
marked when ethyl-groups are introduced, and still more so 
when phenyl- or benzyl-groups are substituted for hydrogen, 
as in the latter case pure blue dyes are produced (see 
below) ; in fact, by varying the number and character of 



528 DYES AND THEIR APPLICATION. 

the substituting groups, almost any shade from red to blue 
can be obtained. 

Lastly, it is interesting to note that when a violet dye, 
like tetramethylrosaniline, combines with an alkyl halogen 
compound, it is converted into a bright-green dye, which, 
however, is somewhat unstable, a